diff --git a/demo/guide-python/continuation.py b/demo/guide-python/continuation.py
index 84afc3710e9e..e32c486651c8 100644
--- a/demo/guide-python/continuation.py
+++ b/demo/guide-python/continuation.py
@@ -16,14 +16,14 @@ def training_continuation(tmpdir: str, use_pickle: bool) -> None:
     """Basic training continuation."""
     # Train 128 iterations in 1 session
     X, y = load_breast_cancer(return_X_y=True)
-    clf = xgboost.XGBClassifier(n_estimators=128)
-    clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss")
+    clf = xgboost.XGBClassifier(n_estimators=128, eval_metric="logloss")
+    clf.fit(X, y, eval_set=[(X, y)])
     print("Total boosted rounds:", clf.get_booster().num_boosted_rounds())
 
     # Train 128 iterations in 2 sessions, with the first one runs for 32 iterations and
     # the second one runs for 96 iterations
-    clf = xgboost.XGBClassifier(n_estimators=32)
-    clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss")
+    clf = xgboost.XGBClassifier(n_estimators=32, eval_metric="logloss")
+    clf.fit(X, y, eval_set=[(X, y)])
     assert clf.get_booster().num_boosted_rounds() == 32
 
     # load back the model, this could be a checkpoint
@@ -39,8 +39,8 @@ def training_continuation(tmpdir: str, use_pickle: bool) -> None:
         loaded = xgboost.XGBClassifier()
         loaded.load_model(path)
 
-    clf = xgboost.XGBClassifier(n_estimators=128 - 32)
-    clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss", xgb_model=loaded)
+    clf = xgboost.XGBClassifier(n_estimators=128 - 32, eval_metric="logloss")
+    clf.fit(X, y, eval_set=[(X, y)], xgb_model=loaded)
 
     print("Total boosted rounds:", clf.get_booster().num_boosted_rounds())
 
@@ -56,19 +56,24 @@ def training_continuation_early_stop(tmpdir: str, use_pickle: bool) -> None:
     n_estimators = 512
 
     X, y = load_breast_cancer(return_X_y=True)
-    clf = xgboost.XGBClassifier(n_estimators=n_estimators)
-    clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss", callbacks=[early_stop])
+    clf = xgboost.XGBClassifier(
+        n_estimators=n_estimators, eval_metric="logloss", callbacks=[early_stop]
+    )
+    clf.fit(X, y, eval_set=[(X, y)])
     print("Total boosted rounds:", clf.get_booster().num_boosted_rounds())
     best = clf.best_iteration
 
     # Train 512 iterations in 2 sessions, with the first one runs for 128 iterations and
     # the second one runs until early stop.
-    clf = xgboost.XGBClassifier(n_estimators=128)
+    clf = xgboost.XGBClassifier(
+        n_estimators=128, eval_metric="logloss", callbacks=[early_stop]
+    )
     # Reinitialize the early stop callback
     early_stop = xgboost.callback.EarlyStopping(
         rounds=early_stopping_rounds, save_best=True
     )
-    clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss", callbacks=[early_stop])
+    clf.set_params(callbacks=[early_stop])
+    clf.fit(X, y, eval_set=[(X, y)])
     assert clf.get_booster().num_boosted_rounds() == 128
 
     # load back the model, this could be a checkpoint
@@ -87,13 +92,13 @@ def training_continuation_early_stop(tmpdir: str, use_pickle: bool) -> None:
     early_stop = xgboost.callback.EarlyStopping(
         rounds=early_stopping_rounds, save_best=True
     )
-    clf = xgboost.XGBClassifier(n_estimators=n_estimators - 128)
+    clf = xgboost.XGBClassifier(
+        n_estimators=n_estimators - 128, eval_metric="logloss", callbacks=[early_stop]
+    )
     clf.fit(
         X,
         y,
         eval_set=[(X, y)],
-        eval_metric="logloss",
-        callbacks=[early_stop],
         xgb_model=loaded,
     )
 
diff --git a/demo/guide-python/sklearn_evals_result.py b/demo/guide-python/sklearn_evals_result.py
index 9aed585007c6..781ab81af722 100644
--- a/demo/guide-python/sklearn_evals_result.py
+++ b/demo/guide-python/sklearn_evals_result.py
@@ -16,30 +16,35 @@
 X_train, X_test = X[:1600], X[1600:]
 y_train, y_test = y[:1600], y[1600:]
 
-param_dist = {'objective':'binary:logistic', 'n_estimators':2}
+param_dist = {"objective": "binary:logistic", "n_estimators": 2}
 
-clf = xgb.XGBModel(**param_dist)
+clf = xgb.XGBModel(
+    **param_dist,
+    eval_metric="logloss",
+)
 # Or you can use: clf = xgb.XGBClassifier(**param_dist)
 
-clf.fit(X_train, y_train,
-        eval_set=[(X_train, y_train), (X_test, y_test)],
-        eval_metric='logloss',
-        verbose=True)
+clf.fit(
+    X_train,
+    y_train,
+    eval_set=[(X_train, y_train), (X_test, y_test)],
+    verbose=True,
+)
 
 # Load evals result by calling the evals_result() function
 evals_result = clf.evals_result()
 
-print('Access logloss metric directly from validation_0:')
-print(evals_result['validation_0']['logloss'])
+print("Access logloss metric directly from validation_0:")
+print(evals_result["validation_0"]["logloss"])
 
-print('')
-print('Access metrics through a loop:')
+print("")
+print("Access metrics through a loop:")
 for e_name, e_mtrs in evals_result.items():
-    print('- {}'.format(e_name))
+    print("- {}".format(e_name))
     for e_mtr_name, e_mtr_vals in e_mtrs.items():
-        print('   - {}'.format(e_mtr_name))
-        print('      - {}'.format(e_mtr_vals))
+        print("   - {}".format(e_mtr_name))
+        print("      - {}".format(e_mtr_vals))
 
-print('')
-print('Access complete dict:')
+print("")
+print("Access complete dict:")
 print(evals_result)
diff --git a/demo/guide-python/sklearn_examples.py b/demo/guide-python/sklearn_examples.py
index cf33e959a119..0fe7a8e24a83 100644
--- a/demo/guide-python/sklearn_examples.py
+++ b/demo/guide-python/sklearn_examples.py
@@ -1,4 +1,4 @@
-'''
+"""
 Collection of examples for using sklearn interface
 ==================================================
 
@@ -8,7 +8,7 @@
 Created on 1 Apr 2015
 
 @author: Jamie Hall
-'''
+"""
 import pickle
 
 import numpy as np
@@ -22,8 +22,8 @@
 
 print("Zeros and Ones from the Digits dataset: binary classification")
 digits = load_digits(n_class=2)
-y = digits['target']
-X = digits['data']
+y = digits["target"]
+X = digits["data"]
 kf = KFold(n_splits=2, shuffle=True, random_state=rng)
 for train_index, test_index in kf.split(X):
     xgb_model = xgb.XGBClassifier(n_jobs=1).fit(X[train_index], y[train_index])
@@ -33,8 +33,8 @@
 
 print("Iris: multiclass classification")
 iris = load_iris()
-y = iris['target']
-X = iris['data']
+y = iris["target"]
+X = iris["data"]
 kf = KFold(n_splits=2, shuffle=True, random_state=rng)
 for train_index, test_index in kf.split(X):
     xgb_model = xgb.XGBClassifier(n_jobs=1).fit(X[train_index], y[train_index])
@@ -53,9 +53,13 @@
 
 print("Parameter optimization")
 xgb_model = xgb.XGBRegressor(n_jobs=1)
-clf = GridSearchCV(xgb_model,
-                   {'max_depth': [2, 4],
-                    'n_estimators': [50, 100]}, verbose=1, n_jobs=1, cv=3)
+clf = GridSearchCV(
+    xgb_model,
+    {"max_depth": [2, 4], "n_estimators": [50, 100]},
+    verbose=1,
+    n_jobs=1,
+    cv=3,
+)
 clf.fit(X, y)
 print(clf.best_score_)
 print(clf.best_params_)
@@ -69,9 +73,8 @@
 
 # Early-stopping
 
-X = digits['data']
-y = digits['target']
+X = digits["data"]
+y = digits["target"]
 X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=0)
-clf = xgb.XGBClassifier(n_jobs=1)
-clf.fit(X_train, y_train, early_stopping_rounds=10, eval_metric="auc",
-        eval_set=[(X_test, y_test)])
+clf = xgb.XGBClassifier(n_jobs=1, early_stopping_rounds=10, eval_metric="auc")
+clf.fit(X_train, y_train, eval_set=[(X_test, y_test)])
diff --git a/demo/guide-python/sklearn_parallel.py b/demo/guide-python/sklearn_parallel.py
index 2ebefffc767f..55e0bff74f08 100644
--- a/demo/guide-python/sklearn_parallel.py
+++ b/demo/guide-python/sklearn_parallel.py
@@ -12,6 +12,7 @@
 if __name__ == "__main__":
     print("Parallel Parameter optimization")
     X, y = fetch_california_housing(return_X_y=True)
+    # Make sure the number of threads is balanced.
     xgb_model = xgb.XGBRegressor(
         n_jobs=multiprocessing.cpu_count() // 2, tree_method="hist"
     )
diff --git a/doc/tutorials/custom_metric_obj.rst b/doc/tutorials/custom_metric_obj.rst
index 118a099c11b3..36bd0c8d65d5 100644
--- a/doc/tutorials/custom_metric_obj.rst
+++ b/doc/tutorials/custom_metric_obj.rst
@@ -123,11 +123,11 @@ monitor our model's performance.  As mentioned above, the default metric for ``S
         elements = np.power(np.log1p(y) - np.log1p(predt), 2)
         return 'PyRMSLE', float(np.sqrt(np.sum(elements) / len(y)))
 
-Since we are demonstrating in Python, the metric or objective need not be a function,
-any callable object should suffice.  Similar to the objective function, our metric also
-accepts ``predt`` and ``dtrain`` as inputs, but returns the name of the metric itself and a
-floating point value as the result.  After passing it into XGBoost as argument of ``feval``
-parameter:
+Since we are demonstrating in Python, the metric or objective need not be a function, any
+callable object should suffice.  Similar to the objective function, our metric also
+accepts ``predt`` and ``dtrain`` as inputs, but returns the name of the metric itself and
+a floating point value as the result.  After passing it into XGBoost as argument of
+``custom_metric`` parameter:
 
 .. code-block:: python
 
@@ -136,7 +136,7 @@ parameter:
               dtrain=dtrain,
               num_boost_round=10,
               obj=squared_log,
-              feval=rmsle,
+              custom_metric=rmsle,
               evals=[(dtrain, 'dtrain'), (dtest, 'dtest')],
               evals_result=results)
 
diff --git a/python-package/xgboost/dask/__init__.py b/python-package/xgboost/dask/__init__.py
index 6b4ae5b075aa..a9b51f35de52 100644
--- a/python-package/xgboost/dask/__init__.py
+++ b/python-package/xgboost/dask/__init__.py
@@ -61,7 +61,7 @@
 import numpy
 
 from xgboost import collective, config
-from xgboost._typing import _T, FeatureNames, FeatureTypes, ModelIn
+from xgboost._typing import _T, FeatureNames, FeatureTypes
 from xgboost.callback import TrainingCallback
 from xgboost.compat import DataFrame, LazyLoader, concat, lazy_isinstance
 from xgboost.core import (
@@ -1774,14 +1774,11 @@ async def _fit_async(
         sample_weight: Optional[_DaskCollection],
         base_margin: Optional[_DaskCollection],
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]],
-        eval_metric: Optional[Union[str, Sequence[str], Metric]],
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]],
         base_margin_eval_set: Optional[Sequence[_DaskCollection]],
-        early_stopping_rounds: Optional[int],
         verbose: Union[int, bool],
         xgb_model: Optional[Union[Booster, XGBModel]],
         feature_weights: Optional[_DaskCollection],
-        callbacks: Optional[Sequence[TrainingCallback]],
     ) -> _DaskCollection:
         params = self.get_xgb_params()
         dtrain, evals = await _async_wrap_evaluation_matrices(
@@ -1809,9 +1806,7 @@ async def _fit_async(
             obj: Optional[Callable] = _objective_decorator(self.objective)
         else:
             obj = None
-        model, metric, params, early_stopping_rounds, callbacks = self._configure_fit(
-            xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-        )
+        model, metric, params = self._configure_fit(xgb_model, params)
         results = await self.client.sync(
             _train_async,
             asynchronous=True,
@@ -1826,8 +1821,8 @@ async def _fit_async(
             feval=None,
             custom_metric=metric,
             verbose_eval=verbose,
-            early_stopping_rounds=early_stopping_rounds,
-            callbacks=callbacks,
+            early_stopping_rounds=self.early_stopping_rounds,
+            callbacks=self.callbacks,
             xgb_model=model,
         )
         self._Booster = results["booster"]
@@ -1844,14 +1839,11 @@ def fit(
         sample_weight: Optional[_DaskCollection] = None,
         base_margin: Optional[_DaskCollection] = None,
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Callable]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Union[int, bool] = True,
         xgb_model: Optional[Union[Booster, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]] = None,
         base_margin_eval_set: Optional[Sequence[_DaskCollection]] = None,
         feature_weights: Optional[_DaskCollection] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "DaskXGBRegressor":
         _assert_dask_support()
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
@@ -1871,14 +1863,11 @@ async def _fit_async(
         sample_weight: Optional[_DaskCollection],
         base_margin: Optional[_DaskCollection],
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]],
-        eval_metric: Optional[Union[str, Sequence[str], Metric]],
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]],
         base_margin_eval_set: Optional[Sequence[_DaskCollection]],
-        early_stopping_rounds: Optional[int],
         verbose: Union[int, bool],
         xgb_model: Optional[Union[Booster, XGBModel]],
         feature_weights: Optional[_DaskCollection],
-        callbacks: Optional[Sequence[TrainingCallback]],
     ) -> "DaskXGBClassifier":
         params = self.get_xgb_params()
         dtrain, evals = await _async_wrap_evaluation_matrices(
@@ -1924,9 +1913,7 @@ async def _fit_async(
             obj: Optional[Callable] = _objective_decorator(self.objective)
         else:
             obj = None
-        model, metric, params, early_stopping_rounds, callbacks = self._configure_fit(
-            xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-        )
+        model, metric, params = self._configure_fit(xgb_model, params)
         results = await self.client.sync(
             _train_async,
             asynchronous=True,
@@ -1941,8 +1928,8 @@ async def _fit_async(
             feval=None,
             custom_metric=metric,
             verbose_eval=verbose,
-            early_stopping_rounds=early_stopping_rounds,
-            callbacks=callbacks,
+            early_stopping_rounds=self.early_stopping_rounds,
+            callbacks=self.callbacks,
             xgb_model=model,
         )
         self._Booster = results["booster"]
@@ -1960,14 +1947,11 @@ def fit(
         sample_weight: Optional[_DaskCollection] = None,
         base_margin: Optional[_DaskCollection] = None,
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Callable]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Union[int, bool] = True,
         xgb_model: Optional[Union[Booster, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]] = None,
         base_margin_eval_set: Optional[Sequence[_DaskCollection]] = None,
         feature_weights: Optional[_DaskCollection] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "DaskXGBClassifier":
         _assert_dask_support()
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
@@ -2063,7 +2047,7 @@ class DaskXGBRanker(DaskScikitLearnBase, XGBRankerMixIn):
     def __init__(self, *, objective: str = "rank:pairwise", **kwargs: Any):
         if callable(objective):
             raise ValueError("Custom objective function not supported by XGBRanker.")
-        super().__init__(objective=objective, kwargs=kwargs)
+        super().__init__(objective=objective, **kwargs)
 
     async def _fit_async(
         self,
@@ -2078,12 +2062,9 @@ async def _fit_async(
         base_margin_eval_set: Optional[Sequence[_DaskCollection]],
         eval_group: Optional[Sequence[_DaskCollection]],
         eval_qid: Optional[Sequence[_DaskCollection]],
-        eval_metric: Optional[Union[str, Sequence[str], Metric]],
-        early_stopping_rounds: Optional[int],
         verbose: Union[int, bool],
         xgb_model: Optional[Union[XGBModel, Booster]],
         feature_weights: Optional[_DaskCollection],
-        callbacks: Optional[Sequence[TrainingCallback]],
     ) -> "DaskXGBRanker":
         msg = "Use `qid` instead of `group` on dask interface."
         if not (group is None and eval_group is None):
@@ -2111,14 +2092,7 @@ async def _fit_async(
             enable_categorical=self.enable_categorical,
             feature_types=self.feature_types,
         )
-        if eval_metric is not None:
-            if callable(eval_metric):
-                raise ValueError(
-                    "Custom evaluation metric is not yet supported for XGBRanker."
-                )
-        model, metric, params, early_stopping_rounds, callbacks = self._configure_fit(
-            xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-        )
+        model, metric, params = self._configure_fit(xgb_model, params)
         results = await self.client.sync(
             _train_async,
             asynchronous=True,
@@ -2133,8 +2107,8 @@ async def _fit_async(
             feval=None,
             custom_metric=metric,
             verbose_eval=verbose,
-            early_stopping_rounds=early_stopping_rounds,
-            callbacks=callbacks,
+            early_stopping_rounds=self.early_stopping_rounds,
+            callbacks=self.callbacks,
             xgb_model=model,
         )
         self._Booster = results["booster"]
@@ -2155,14 +2129,11 @@ def fit(
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]] = None,
         eval_group: Optional[Sequence[_DaskCollection]] = None,
         eval_qid: Optional[Sequence[_DaskCollection]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Callable]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Union[int, bool] = False,
         xgb_model: Optional[Union[XGBModel, Booster]] = None,
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]] = None,
         base_margin_eval_set: Optional[Sequence[_DaskCollection]] = None,
         feature_weights: Optional[_DaskCollection] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "DaskXGBRanker":
         _assert_dask_support()
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
@@ -2221,18 +2192,15 @@ def fit(
         sample_weight: Optional[_DaskCollection] = None,
         base_margin: Optional[_DaskCollection] = None,
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Callable]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Union[int, bool] = True,
         xgb_model: Optional[Union[Booster, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]] = None,
         base_margin_eval_set: Optional[Sequence[_DaskCollection]] = None,
         feature_weights: Optional[_DaskCollection] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "DaskXGBRFRegressor":
         _assert_dask_support()
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
-        _check_rf_callback(early_stopping_rounds, callbacks)
+        _check_rf_callback(self.early_stopping_rounds, self.callbacks)
         super().fit(**args)
         return self
 
@@ -2285,17 +2253,14 @@ def fit(
         sample_weight: Optional[_DaskCollection] = None,
         base_margin: Optional[_DaskCollection] = None,
         eval_set: Optional[Sequence[Tuple[_DaskCollection, _DaskCollection]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Callable]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Union[int, bool] = True,
         xgb_model: Optional[Union[Booster, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[_DaskCollection]] = None,
         base_margin_eval_set: Optional[Sequence[_DaskCollection]] = None,
         feature_weights: Optional[_DaskCollection] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "DaskXGBRFClassifier":
         _assert_dask_support()
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
-        _check_rf_callback(early_stopping_rounds, callbacks)
+        _check_rf_callback(self.early_stopping_rounds, self.callbacks)
         super().fit(**args)
         return self
diff --git a/python-package/xgboost/sklearn.py b/python-package/xgboost/sklearn.py
index 8c3a96784af6..a0fde2292323 100644
--- a/python-package/xgboost/sklearn.py
+++ b/python-package/xgboost/sklearn.py
@@ -349,12 +349,6 @@ def task(i: int) -> float:
         See :doc:`/tutorials/custom_metric_obj` and :ref:`custom-obj-metric` for more
         information.
 
-        .. note::
-
-             This parameter replaces `eval_metric` in :py:meth:`fit` method.  The old
-             one receives un-transformed prediction regardless of whether custom
-             objective is being used.
-
         .. code-block:: python
 
             from sklearn.datasets import load_diabetes
@@ -389,10 +383,6 @@ def task(i: int) -> float:
           early stopping.  If there's more than one metric in **eval_metric**, the last
           metric will be used for early stopping.
 
-        .. note::
-
-            This parameter replaces `early_stopping_rounds` in :py:meth:`fit` method.
-
     callbacks : Optional[List[TrainingCallback]]
         List of callback functions that are applied at end of each iteration.
         It is possible to use predefined callbacks by using
@@ -872,16 +862,11 @@ def _load_model_attributes(self, config: dict) -> None:
     def _configure_fit(
         self,
         booster: Optional[Union[Booster, "XGBModel", str]],
-        eval_metric: Optional[Union[Callable, str, Sequence[str]]],
         params: Dict[str, Any],
-        early_stopping_rounds: Optional[int],
-        callbacks: Optional[Sequence[TrainingCallback]],
     ) -> Tuple[
         Optional[Union[Booster, str, "XGBModel"]],
         Optional[Metric],
         Dict[str, Any],
-        Optional[int],
-        Optional[Sequence[TrainingCallback]],
     ]:
         """Configure parameters for :py:meth:`fit`."""
         if isinstance(booster, XGBModel):
@@ -903,49 +888,16 @@ def _duplicated(parameter: str) -> None:
                 "or `set_params` instead."
             )
 
-        # Configure evaluation metric.
-        if eval_metric is not None:
-            _deprecated("eval_metric")
-        if self.eval_metric is not None and eval_metric is not None:
-            _duplicated("eval_metric")
-        # - track where does the evaluation metric come from
-        if self.eval_metric is not None:
-            from_fit = False
-            eval_metric = self.eval_metric
-        else:
-            from_fit = True
         # - configure callable evaluation metric
         metric: Optional[Metric] = None
-        if eval_metric is not None:
-            if callable(eval_metric) and from_fit:
-                # No need to wrap the evaluation function for old parameter.
-                metric = eval_metric
-            elif callable(eval_metric):
-                # Parameter from constructor or set_params
+        if self.eval_metric is not None:
+            if callable(self.eval_metric):
                 if self._get_type() == "ranker":
-                    metric = ltr_metric_decorator(eval_metric, self.n_jobs)
+                    metric = ltr_metric_decorator(self.eval_metric, self.n_jobs)
                 else:
-                    metric = _metric_decorator(eval_metric)
+                    metric = _metric_decorator(self.eval_metric)
             else:
-                params.update({"eval_metric": eval_metric})
-
-        # Configure early_stopping_rounds
-        if early_stopping_rounds is not None:
-            _deprecated("early_stopping_rounds")
-        if early_stopping_rounds is not None and self.early_stopping_rounds is not None:
-            _duplicated("early_stopping_rounds")
-        early_stopping_rounds = (
-            self.early_stopping_rounds
-            if self.early_stopping_rounds is not None
-            else early_stopping_rounds
-        )
-
-        # Configure callbacks
-        if callbacks is not None:
-            _deprecated("callbacks")
-        if callbacks is not None and self.callbacks is not None:
-            _duplicated("callbacks")
-        callbacks = self.callbacks if self.callbacks is not None else callbacks
+                params.update({"eval_metric": self.eval_metric})
 
         tree_method = params.get("tree_method", None)
         if self.enable_categorical and tree_method == "exact":
@@ -953,7 +905,7 @@ def _duplicated(parameter: str) -> None:
                 "Experimental support for categorical data is not implemented for"
                 " current tree method yet."
             )
-        return model, metric, params, early_stopping_rounds, callbacks
+        return model, metric, params
 
     def _create_dmatrix(self, ref: Optional[DMatrix], **kwargs: Any) -> DMatrix:
         # Use `QuantileDMatrix` to save memory.
@@ -979,14 +931,11 @@ def fit(
         sample_weight: Optional[ArrayLike] = None,
         base_margin: Optional[ArrayLike] = None,
         eval_set: Optional[Sequence[Tuple[ArrayLike, ArrayLike]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Metric]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Optional[Union[bool, int]] = True,
         xgb_model: Optional[Union[Booster, str, "XGBModel"]] = None,
         sample_weight_eval_set: Optional[Sequence[ArrayLike]] = None,
         base_margin_eval_set: Optional[Sequence[ArrayLike]] = None,
         feature_weights: Optional[ArrayLike] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "XGBModel":
         # pylint: disable=invalid-name,attribute-defined-outside-init
         """Fit gradient boosting model.
@@ -1017,18 +966,6 @@ def fit(
             metrics will be computed.
             Validation metrics will help us track the performance of the model.
 
-        eval_metric : str, list of str, or callable, optional
-
-            .. deprecated:: 1.6.0
-
-            Use `eval_metric` in :py:meth:`__init__` or :py:meth:`set_params` instead.
-
-        early_stopping_rounds : int
-
-            .. deprecated:: 1.6.0
-
-            Use `early_stopping_rounds` in :py:meth:`__init__` or :py:meth:`set_params`
-            instead.
         verbose :
             If `verbose` is True and an evaluation set is used, the evaluation metric
             measured on the validation set is printed to stdout at each boosting stage.
@@ -1049,10 +986,6 @@ def fit(
             selected when colsample is being used.  All values must be greater than 0,
             otherwise a `ValueError` is thrown.
 
-        callbacks :
-            .. deprecated:: 1.6.0
-                Use `callbacks` in :py:meth:`__init__` or :py:meth:`set_params` instead.
-
         """
         with config_context(verbosity=self.verbosity):
             evals_result: TrainingCallback.EvalsLog = {}
@@ -1082,27 +1015,19 @@ def fit(
             else:
                 obj = None
 
-            (
-                model,
-                metric,
-                params,
-                early_stopping_rounds,
-                callbacks,
-            ) = self._configure_fit(
-                xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-            )
+            model, metric, params = self._configure_fit(xgb_model, params)
             self._Booster = train(
                 params,
                 train_dmatrix,
                 self.get_num_boosting_rounds(),
                 evals=evals,
-                early_stopping_rounds=early_stopping_rounds,
+                early_stopping_rounds=self.early_stopping_rounds,
                 evals_result=evals_result,
                 obj=obj,
                 custom_metric=metric,
                 verbose_eval=verbose,
                 xgb_model=model,
-                callbacks=callbacks,
+                callbacks=self.callbacks,
             )
 
             self._set_evaluation_result(evals_result)
@@ -1437,14 +1362,11 @@ def fit(
         sample_weight: Optional[ArrayLike] = None,
         base_margin: Optional[ArrayLike] = None,
         eval_set: Optional[Sequence[Tuple[ArrayLike, ArrayLike]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Metric]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Optional[Union[bool, int]] = True,
         xgb_model: Optional[Union[Booster, str, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[ArrayLike]] = None,
         base_margin_eval_set: Optional[Sequence[ArrayLike]] = None,
         feature_weights: Optional[ArrayLike] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "XGBClassifier":
         # pylint: disable = attribute-defined-outside-init,too-many-statements
         with config_context(verbosity=self.verbosity):
@@ -1492,15 +1414,7 @@ def fit(
                     params["objective"] = "multi:softprob"
                 params["num_class"] = self.n_classes_
 
-            (
-                model,
-                metric,
-                params,
-                early_stopping_rounds,
-                callbacks,
-            ) = self._configure_fit(
-                xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-            )
+            model, metric, params = self._configure_fit(xgb_model, params)
             train_dmatrix, evals = _wrap_evaluation_matrices(
                 missing=self.missing,
                 X=X,
@@ -1525,13 +1439,13 @@ def fit(
                 train_dmatrix,
                 self.get_num_boosting_rounds(),
                 evals=evals,
-                early_stopping_rounds=early_stopping_rounds,
+                early_stopping_rounds=self.early_stopping_rounds,
                 evals_result=evals_result,
                 obj=obj,
                 custom_metric=metric,
                 verbose_eval=verbose,
                 xgb_model=model,
-                callbacks=callbacks,
+                callbacks=self.callbacks,
             )
 
             if not callable(self.objective):
@@ -1693,17 +1607,14 @@ def fit(
         sample_weight: Optional[ArrayLike] = None,
         base_margin: Optional[ArrayLike] = None,
         eval_set: Optional[Sequence[Tuple[ArrayLike, ArrayLike]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Metric]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Optional[Union[bool, int]] = True,
         xgb_model: Optional[Union[Booster, str, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[ArrayLike]] = None,
         base_margin_eval_set: Optional[Sequence[ArrayLike]] = None,
         feature_weights: Optional[ArrayLike] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "XGBRFClassifier":
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
-        _check_rf_callback(early_stopping_rounds, callbacks)
+        _check_rf_callback(self.early_stopping_rounds, self.callbacks)
         super().fit(**args)
         return self
 
@@ -1768,17 +1679,14 @@ def fit(
         sample_weight: Optional[ArrayLike] = None,
         base_margin: Optional[ArrayLike] = None,
         eval_set: Optional[Sequence[Tuple[ArrayLike, ArrayLike]]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Metric]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Optional[Union[bool, int]] = True,
         xgb_model: Optional[Union[Booster, str, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[ArrayLike]] = None,
         base_margin_eval_set: Optional[Sequence[ArrayLike]] = None,
         feature_weights: Optional[ArrayLike] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "XGBRFRegressor":
         args = {k: v for k, v in locals().items() if k not in ("self", "__class__")}
-        _check_rf_callback(early_stopping_rounds, callbacks)
+        _check_rf_callback(self.early_stopping_rounds, self.callbacks)
         super().fit(**args)
         return self
 
@@ -1883,14 +1791,11 @@ def fit(
         eval_set: Optional[Sequence[Tuple[ArrayLike, ArrayLike]]] = None,
         eval_group: Optional[Sequence[ArrayLike]] = None,
         eval_qid: Optional[Sequence[ArrayLike]] = None,
-        eval_metric: Optional[Union[str, Sequence[str], Metric]] = None,
-        early_stopping_rounds: Optional[int] = None,
         verbose: Optional[Union[bool, int]] = False,
         xgb_model: Optional[Union[Booster, str, XGBModel]] = None,
         sample_weight_eval_set: Optional[Sequence[ArrayLike]] = None,
         base_margin_eval_set: Optional[Sequence[ArrayLike]] = None,
         feature_weights: Optional[ArrayLike] = None,
-        callbacks: Optional[Sequence[TrainingCallback]] = None,
     ) -> "XGBRanker":
         # pylint: disable = attribute-defined-outside-init,arguments-differ
         """Fit gradient boosting ranker
@@ -1960,15 +1865,6 @@ def fit(
             pair in **eval_set**. The special column convention in `X` applies to
             validation datasets as well.
 
-        eval_metric : str, list of str, optional
-            .. deprecated:: 1.6.0
-                use `eval_metric` in :py:meth:`__init__` or :py:meth:`set_params` instead.
-
-        early_stopping_rounds : int
-            .. deprecated:: 1.6.0
-                use `early_stopping_rounds` in :py:meth:`__init__` or
-                :py:meth:`set_params` instead.
-
         verbose :
             If `verbose` is True and an evaluation set is used, the evaluation metric
             measured on the validation set is printed to stdout at each boosting stage.
@@ -1996,10 +1892,6 @@ def fit(
             selected when colsample is being used.  All values must be greater than 0,
             otherwise a `ValueError` is thrown.
 
-        callbacks :
-            .. deprecated:: 1.6.0
-                Use `callbacks` in :py:meth:`__init__` or :py:meth:`set_params` instead.
-
         """
         with config_context(verbosity=self.verbosity):
             train_dmatrix, evals = _wrap_evaluation_matrices(
@@ -2024,27 +1916,19 @@ def fit(
             evals_result: TrainingCallback.EvalsLog = {}
             params = self.get_xgb_params()
 
-            (
-                model,
-                metric,
-                params,
-                early_stopping_rounds,
-                callbacks,
-            ) = self._configure_fit(
-                xgb_model, eval_metric, params, early_stopping_rounds, callbacks
-            )
+            model, metric, params = self._configure_fit(xgb_model, params)
 
             self._Booster = train(
                 params,
                 train_dmatrix,
                 num_boost_round=self.get_num_boosting_rounds(),
-                early_stopping_rounds=early_stopping_rounds,
+                early_stopping_rounds=self.early_stopping_rounds,
                 evals=evals,
                 evals_result=evals_result,
                 custom_metric=metric,
                 verbose_eval=verbose,
                 xgb_model=model,
-                callbacks=callbacks,
+                callbacks=self.callbacks,
             )
 
             self.objective = params["objective"]
diff --git a/tests/ci_build/lint_python.py b/tests/ci_build/lint_python.py
index 87d76607f984..bd9b9bedb39a 100644
--- a/tests/ci_build/lint_python.py
+++ b/tests/ci_build/lint_python.py
@@ -18,10 +18,12 @@ class LintersPaths:
         "python-package/",
         # tests
         "tests/python/test_config.py",
+        "tests/python/test_callback.py",
         "tests/python/test_data_iterator.py",
         "tests/python/test_dmatrix.py",
         "tests/python/test_dt.py",
         "tests/python/test_demos.py",
+        "tests/python/test_eval_metrics.py",
         "tests/python/test_multi_target.py",
         "tests/python/test_predict.py",
         "tests/python/test_quantile_dmatrix.py",
@@ -39,12 +41,15 @@ class LintersPaths:
         "demo/dask/",
         "demo/rmm_plugin",
         "demo/json-model/json_parser.py",
+        "demo/guide-python/continuation.py",
         "demo/guide-python/cat_in_the_dat.py",
         "demo/guide-python/callbacks.py",
         "demo/guide-python/categorical.py",
         "demo/guide-python/cat_pipeline.py",
         "demo/guide-python/feature_weights.py",
         "demo/guide-python/sklearn_parallel.py",
+        "demo/guide-python/sklearn_examples.py",
+        "demo/guide-python/sklearn_evals_result.py",
         "demo/guide-python/spark_estimator_examples.py",
         "demo/guide-python/external_memory.py",
         "demo/guide-python/individual_trees.py",
@@ -93,6 +98,7 @@ class LintersPaths:
         # demo
         "demo/json-model/json_parser.py",
         "demo/guide-python/external_memory.py",
+        "demo/guide-python/continuation.py",
         "demo/guide-python/callbacks.py",
         "demo/guide-python/cat_in_the_dat.py",
         "demo/guide-python/categorical.py",
diff --git a/tests/python/test_callback.py b/tests/python/test_callback.py
index 3a7501e48383..d2e7cb5c4b8e 100644
--- a/tests/python/test_callback.py
+++ b/tests/python/test_callback.py
@@ -16,13 +16,14 @@ class TestCallbacks:
     @classmethod
     def setup_class(cls):
         from sklearn.datasets import load_breast_cancer
+
         X, y = load_breast_cancer(return_X_y=True)
         cls.X = X
         cls.y = y
 
-        split = int(X.shape[0]*0.8)
-        cls.X_train = X[: split, ...]
-        cls.y_train = y[: split, ...]
+        split = int(X.shape[0] * 0.8)
+        cls.X_train = X[:split, ...]
+        cls.y_train = y[:split, ...]
         cls.X_valid = X[split:, ...]
         cls.y_valid = y[split:, ...]
 
@@ -31,31 +32,32 @@ def run_evaluation_monitor(
         D_train: xgb.DMatrix,
         D_valid: xgb.DMatrix,
         rounds: int,
-        verbose_eval: Union[bool, int]
+        verbose_eval: Union[bool, int],
     ):
         def check_output(output: str) -> None:
             if int(verbose_eval) == 1:
                 # Should print each iteration info
-                assert len(output.split('\n')) == rounds
+                assert len(output.split("\n")) == rounds
             elif int(verbose_eval) > rounds:
                 # Should print first and latest iteration info
-                assert len(output.split('\n')) == 2
+                assert len(output.split("\n")) == 2
             else:
                 # Should print info by each period additionaly to first and latest
                 # iteration
                 num_periods = rounds // int(verbose_eval)
                 # Extra information is required for latest iteration
                 is_extra_info_required = num_periods * int(verbose_eval) < (rounds - 1)
-                assert len(output.split('\n')) == (
+                assert len(output.split("\n")) == (
                     1 + num_periods + int(is_extra_info_required)
                 )
 
         evals_result: xgb.callback.TrainingCallback.EvalsLog = {}
-        params = {'objective': 'binary:logistic', 'eval_metric': 'error'}
+        params = {"objective": "binary:logistic", "eval_metric": "error"}
         with tm.captured_output() as (out, err):
             xgb.train(
-                params, D_train,
-                evals=[(D_train, 'Train'), (D_valid, 'Valid')],
+                params,
+                D_train,
+                evals=[(D_train, "Train"), (D_valid, "Valid")],
                 num_boost_round=rounds,
                 evals_result=evals_result,
                 verbose_eval=verbose_eval,
@@ -73,14 +75,16 @@ def test_evaluation_monitor(self):
         D_valid = xgb.DMatrix(self.X_valid, self.y_valid)
         evals_result = {}
         rounds = 10
-        xgb.train({'objective': 'binary:logistic',
-                   'eval_metric': 'error'}, D_train,
-                  evals=[(D_train, 'Train'), (D_valid, 'Valid')],
-                  num_boost_round=rounds,
-                  evals_result=evals_result,
-                  verbose_eval=True)
-        assert len(evals_result['Train']['error']) == rounds
-        assert len(evals_result['Valid']['error']) == rounds
+        xgb.train(
+            {"objective": "binary:logistic", "eval_metric": "error"},
+            D_train,
+            evals=[(D_train, "Train"), (D_valid, "Valid")],
+            num_boost_round=rounds,
+            evals_result=evals_result,
+            verbose_eval=True,
+        )
+        assert len(evals_result["Train"]["error"]) == rounds
+        assert len(evals_result["Valid"]["error"]) == rounds
 
         self.run_evaluation_monitor(D_train, D_valid, rounds, True)
         self.run_evaluation_monitor(D_train, D_valid, rounds, 2)
@@ -93,72 +97,83 @@ def test_early_stopping(self):
         evals_result = {}
         rounds = 30
         early_stopping_rounds = 5
-        booster = xgb.train({'objective': 'binary:logistic',
-                             'eval_metric': 'error'}, D_train,
-                            evals=[(D_train, 'Train'), (D_valid, 'Valid')],
-                            num_boost_round=rounds,
-                            evals_result=evals_result,
-                            verbose_eval=True,
-                            early_stopping_rounds=early_stopping_rounds)
-        dump = booster.get_dump(dump_format='json')
+        booster = xgb.train(
+            {"objective": "binary:logistic", "eval_metric": "error"},
+            D_train,
+            evals=[(D_train, "Train"), (D_valid, "Valid")],
+            num_boost_round=rounds,
+            evals_result=evals_result,
+            verbose_eval=True,
+            early_stopping_rounds=early_stopping_rounds,
+        )
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) - booster.best_iteration == early_stopping_rounds + 1
 
     def test_early_stopping_custom_eval(self):
         D_train = xgb.DMatrix(self.X_train, self.y_train)
         D_valid = xgb.DMatrix(self.X_valid, self.y_valid)
         early_stopping_rounds = 5
-        booster = xgb.train({'objective': 'binary:logistic',
-                             'eval_metric': 'error',
-                             'tree_method': 'hist'}, D_train,
-                            evals=[(D_train, 'Train'), (D_valid, 'Valid')],
-                            feval=tm.eval_error_metric,
-                            num_boost_round=1000,
-                            early_stopping_rounds=early_stopping_rounds,
-                            verbose_eval=False)
-        dump = booster.get_dump(dump_format='json')
+        booster = xgb.train(
+            {
+                "objective": "binary:logistic",
+                "eval_metric": "error",
+                "tree_method": "hist",
+            },
+            D_train,
+            evals=[(D_train, "Train"), (D_valid, "Valid")],
+            feval=tm.eval_error_metric,
+            num_boost_round=1000,
+            early_stopping_rounds=early_stopping_rounds,
+            verbose_eval=False,
+        )
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) - booster.best_iteration == early_stopping_rounds + 1
 
     def test_early_stopping_customize(self):
         D_train = xgb.DMatrix(self.X_train, self.y_train)
         D_valid = xgb.DMatrix(self.X_valid, self.y_valid)
         early_stopping_rounds = 5
-        early_stop = xgb.callback.EarlyStopping(rounds=early_stopping_rounds,
-                                                metric_name='CustomErr',
-                                                data_name='Train')
+        early_stop = xgb.callback.EarlyStopping(
+            rounds=early_stopping_rounds, metric_name="CustomErr", data_name="Train"
+        )
         # Specify which dataset and which metric should be used for early stopping.
         booster = xgb.train(
-            {'objective': 'binary:logistic',
-             'eval_metric': ['error', 'rmse'],
-             'tree_method': 'hist'}, D_train,
-            evals=[(D_train, 'Train'), (D_valid, 'Valid')],
+            {
+                "objective": "binary:logistic",
+                "eval_metric": ["error", "rmse"],
+                "tree_method": "hist",
+            },
+            D_train,
+            evals=[(D_train, "Train"), (D_valid, "Valid")],
             feval=tm.eval_error_metric,
             num_boost_round=1000,
             callbacks=[early_stop],
-            verbose_eval=False)
-        dump = booster.get_dump(dump_format='json')
+            verbose_eval=False,
+        )
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) - booster.best_iteration == early_stopping_rounds + 1
-        assert len(early_stop.stopping_history['Train']['CustomErr']) == len(dump)
+        assert len(early_stop.stopping_history["Train"]["CustomErr"]) == len(dump)
 
         rounds = 100
         early_stop = xgb.callback.EarlyStopping(
             rounds=early_stopping_rounds,
-            metric_name='CustomErr',
-            data_name='Train',
+            metric_name="CustomErr",
+            data_name="Train",
             min_delta=100,
             save_best=True,
         )
         booster = xgb.train(
             {
-                'objective': 'binary:logistic',
-                'eval_metric': ['error', 'rmse'],
-                'tree_method': 'hist'
+                "objective": "binary:logistic",
+                "eval_metric": ["error", "rmse"],
+                "tree_method": "hist",
             },
             D_train,
-            evals=[(D_train, 'Train'), (D_valid, 'Valid')],
+            evals=[(D_train, "Train"), (D_valid, "Valid")],
             feval=tm.eval_error_metric,
             num_boost_round=rounds,
             callbacks=[early_stop],
-            verbose_eval=False
+            verbose_eval=False,
         )
         # No iteration can be made with min_delta == 100
         assert booster.best_iteration == 0
@@ -166,18 +181,20 @@ def test_early_stopping_customize(self):
 
     def test_early_stopping_skl(self):
         from sklearn.datasets import load_breast_cancer
+
         X, y = load_breast_cancer(return_X_y=True)
         early_stopping_rounds = 5
         cls = xgb.XGBClassifier(
-            early_stopping_rounds=early_stopping_rounds, eval_metric='error'
+            early_stopping_rounds=early_stopping_rounds, eval_metric="error"
         )
         cls.fit(X, y, eval_set=[(X, y)])
         booster = cls.get_booster()
-        dump = booster.get_dump(dump_format='json')
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) - booster.best_iteration == early_stopping_rounds + 1
 
     def test_early_stopping_custom_eval_skl(self):
         from sklearn.datasets import load_breast_cancer
+
         X, y = load_breast_cancer(return_X_y=True)
         early_stopping_rounds = 5
         early_stop = xgb.callback.EarlyStopping(rounds=early_stopping_rounds)
@@ -186,11 +203,12 @@ def test_early_stopping_custom_eval_skl(self):
         )
         cls.fit(X, y, eval_set=[(X, y)])
         booster = cls.get_booster()
-        dump = booster.get_dump(dump_format='json')
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) - booster.best_iteration == early_stopping_rounds + 1
 
     def test_early_stopping_save_best_model(self):
         from sklearn.datasets import load_breast_cancer
+
         X, y = load_breast_cancer(return_X_y=True)
         n_estimators = 100
         early_stopping_rounds = 5
@@ -200,11 +218,11 @@ def test_early_stopping_save_best_model(self):
         cls = xgb.XGBClassifier(
             n_estimators=n_estimators,
             eval_metric=tm.eval_error_metric_skl,
-            callbacks=[early_stop]
+            callbacks=[early_stop],
         )
         cls.fit(X, y, eval_set=[(X, y)])
         booster = cls.get_booster()
-        dump = booster.get_dump(dump_format='json')
+        dump = booster.get_dump(dump_format="json")
         assert len(dump) == booster.best_iteration + 1
 
         early_stop = xgb.callback.EarlyStopping(
@@ -220,8 +238,9 @@ def test_early_stopping_save_best_model(self):
             cls.fit(X, y, eval_set=[(X, y)])
 
         # No error
-        early_stop = xgb.callback.EarlyStopping(rounds=early_stopping_rounds,
-                                                save_best=False)
+        early_stop = xgb.callback.EarlyStopping(
+            rounds=early_stopping_rounds, save_best=False
+        )
         xgb.XGBClassifier(
             booster="gblinear",
             n_estimators=10,
@@ -231,14 +250,17 @@ def test_early_stopping_save_best_model(self):
 
     def test_early_stopping_continuation(self):
         from sklearn.datasets import load_breast_cancer
+
         X, y = load_breast_cancer(return_X_y=True)
-        cls = xgb.XGBClassifier(eval_metric=tm.eval_error_metric_skl)
+
         early_stopping_rounds = 5
         early_stop = xgb.callback.EarlyStopping(
             rounds=early_stopping_rounds, save_best=True
         )
-        with pytest.warns(UserWarning):
-            cls.fit(X, y, eval_set=[(X, y)], callbacks=[early_stop])
+        cls = xgb.XGBClassifier(
+            eval_metric=tm.eval_error_metric_skl, callbacks=[early_stop]
+        )
+        cls.fit(X, y, eval_set=[(X, y)])
 
         booster = cls.get_booster()
         assert booster.num_boosted_rounds() == booster.best_iteration + 1
@@ -256,21 +278,10 @@ def test_early_stopping_continuation(self):
             )
             cls.fit(X, y, eval_set=[(X, y)])
             booster = cls.get_booster()
-            assert booster.num_boosted_rounds() == \
-                booster.best_iteration + early_stopping_rounds + 1
-
-    def test_deprecated(self):
-        from sklearn.datasets import load_breast_cancer
-        X, y = load_breast_cancer(return_X_y=True)
-        early_stopping_rounds = 5
-        early_stop = xgb.callback.EarlyStopping(
-            rounds=early_stopping_rounds, save_best=True
-        )
-        clf = xgb.XGBClassifier(
-            eval_metric=tm.eval_error_metric_skl, callbacks=[early_stop]
-        )
-        with pytest.raises(ValueError, match=r".*set_params.*"):
-            clf.fit(X, y, eval_set=[(X, y)], callbacks=[early_stop])
+            assert (
+                booster.num_boosted_rounds()
+                == booster.best_iteration + early_stopping_rounds + 1
+            )
 
     def run_eta_decay(self, tree_method):
         """Test learning rate scheduler, used by both CPU and GPU tests."""
@@ -343,7 +354,7 @@ def run_eta_decay(self, tree_method):
             callbacks=[scheduler([0, 0, 0, 0])],
             evals_result=evals_result,
         )
-        eval_errors_2 = list(map(float, evals_result['eval']['error']))
+        eval_errors_2 = list(map(float, evals_result["eval"]["error"]))
         assert isinstance(bst, xgb.core.Booster)
         # validation error should not decrease, if eta/learning_rate = 0
         assert eval_errors_2[0] == eval_errors_2[-1]
@@ -361,7 +372,7 @@ def eta_decay(ithround, num_boost_round=num_round):
             callbacks=[scheduler(eta_decay)],
             evals_result=evals_result,
         )
-        eval_errors_3 = list(map(float, evals_result['eval']['error']))
+        eval_errors_3 = list(map(float, evals_result["eval"]["error"]))
 
         assert isinstance(bst, xgb.core.Booster)
 
diff --git a/tests/python/test_early_stopping.py b/tests/python/test_early_stopping.py
index 7695c6861c94..a275a8077b71 100644
--- a/tests/python/test_early_stopping.py
+++ b/tests/python/test_early_stopping.py
@@ -15,23 +15,23 @@ def test_early_stopping_nonparallel(self):
         from sklearn.model_selection import train_test_split
 
         digits = load_digits(n_class=2)
-        X = digits['data']
-        y = digits['target']
+        X = digits["data"]
+        y = digits["target"]
         X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=0)
-        clf1 = xgb.XGBClassifier(learning_rate=0.1)
-        clf1.fit(X_train, y_train, early_stopping_rounds=5, eval_metric="auc",
-                 eval_set=[(X_test, y_test)])
-        clf2 = xgb.XGBClassifier(learning_rate=0.1)
-        clf2.fit(X_train, y_train, early_stopping_rounds=4, eval_metric="auc",
-                 eval_set=[(X_test, y_test)])
+        clf1 = xgb.XGBClassifier(
+            learning_rate=0.1, early_stopping_rounds=5, eval_metric="auc"
+        )
+        clf1.fit(X_train, y_train, eval_set=[(X_test, y_test)])
+        clf2 = xgb.XGBClassifier(
+            learning_rate=0.1, early_stopping_rounds=4, eval_metric="auc"
+        )
+        clf2.fit(X_train, y_train, eval_set=[(X_test, y_test)])
         # should be the same
         assert clf1.best_score == clf2.best_score
         assert clf1.best_score != 1
         # check overfit
         clf3 = xgb.XGBClassifier(
-            learning_rate=0.1,
-            eval_metric="auc",
-            early_stopping_rounds=10
+            learning_rate=0.1, eval_metric="auc", early_stopping_rounds=10
         )
         clf3.fit(X_train, y_train, eval_set=[(X_test, y_test)])
         base_score = get_basescore(clf3)
@@ -39,9 +39,9 @@ def test_early_stopping_nonparallel(self):
 
         clf3 = xgb.XGBClassifier(
             learning_rate=0.1,
-            base_score=.5,
+            base_score=0.5,
             eval_metric="auc",
-            early_stopping_rounds=10
+            early_stopping_rounds=10,
         )
         clf3.fit(X_train, y_train, eval_set=[(X_test, y_test)])
 
diff --git a/tests/python/test_eval_metrics.py b/tests/python/test_eval_metrics.py
index 92726014b7dc..cbb3dc88d792 100644
--- a/tests/python/test_eval_metrics.py
+++ b/tests/python/test_eval_metrics.py
@@ -9,37 +9,41 @@
 
 
 class TestEvalMetrics:
-    xgb_params_01 = {'nthread': 1, 'eval_metric': 'error'}
+    xgb_params_01 = {"nthread": 1, "eval_metric": "error"}
 
-    xgb_params_02 = {'nthread': 1, 'eval_metric': ['error']}
+    xgb_params_02 = {"nthread": 1, "eval_metric": ["error"]}
 
-    xgb_params_03 = {'nthread': 1, 'eval_metric': ['rmse', 'error']}
+    xgb_params_03 = {"nthread": 1, "eval_metric": ["rmse", "error"]}
 
-    xgb_params_04 = {'nthread': 1, 'eval_metric': ['error', 'rmse']}
+    xgb_params_04 = {"nthread": 1, "eval_metric": ["error", "rmse"]}
 
     def evalerror_01(self, preds, dtrain):
         labels = dtrain.get_label()
-        return 'error', float(sum(labels != (preds > 0.0))) / len(labels)
+        return "error", float(sum(labels != (preds > 0.0))) / len(labels)
 
     def evalerror_02(self, preds, dtrain):
         labels = dtrain.get_label()
-        return [('error', float(sum(labels != (preds > 0.0))) / len(labels))]
+        return [("error", float(sum(labels != (preds > 0.0))) / len(labels))]
 
     @pytest.mark.skipif(**tm.no_sklearn())
     def evalerror_03(self, preds, dtrain):
         from sklearn.metrics import mean_squared_error
 
         labels = dtrain.get_label()
-        return [('rmse', mean_squared_error(labels, preds)),
-                ('error', float(sum(labels != (preds > 0.0))) / len(labels))]
+        return [
+            ("rmse", mean_squared_error(labels, preds)),
+            ("error", float(sum(labels != (preds > 0.0))) / len(labels)),
+        ]
 
     @pytest.mark.skipif(**tm.no_sklearn())
     def evalerror_04(self, preds, dtrain):
         from sklearn.metrics import mean_squared_error
 
         labels = dtrain.get_label()
-        return [('error', float(sum(labels != (preds > 0.0))) / len(labels)),
-                ('rmse', mean_squared_error(labels, preds))]
+        return [
+            ("error", float(sum(labels != (preds > 0.0))) / len(labels)),
+            ("rmse", mean_squared_error(labels, preds)),
+        ]
 
     @pytest.mark.skipif(**tm.no_sklearn())
     def test_eval_metrics(self):
@@ -50,15 +54,15 @@ def test_eval_metrics(self):
         from sklearn.datasets import load_digits
 
         digits = load_digits(n_class=2)
-        X = digits['data']
-        y = digits['target']
+        X = digits["data"]
+        y = digits["target"]
 
         Xt, Xv, yt, yv = train_test_split(X, y, test_size=0.2, random_state=0)
 
         dtrain = xgb.DMatrix(Xt, label=yt)
         dvalid = xgb.DMatrix(Xv, label=yv)
 
-        watchlist = [(dtrain, 'train'), (dvalid, 'val')]
+        watchlist = [(dtrain, "train"), (dvalid, "val")]
 
         gbdt_01 = xgb.train(self.xgb_params_01, dtrain, num_boost_round=10)
         gbdt_02 = xgb.train(self.xgb_params_02, dtrain, num_boost_round=10)
@@ -66,26 +70,54 @@ def test_eval_metrics(self):
         assert gbdt_01.predict(dvalid)[0] == gbdt_02.predict(dvalid)[0]
         assert gbdt_01.predict(dvalid)[0] == gbdt_03.predict(dvalid)[0]
 
-        gbdt_01 = xgb.train(self.xgb_params_01, dtrain, 10, watchlist,
-                            early_stopping_rounds=2)
-        gbdt_02 = xgb.train(self.xgb_params_02, dtrain, 10, watchlist,
-                            early_stopping_rounds=2)
-        gbdt_03 = xgb.train(self.xgb_params_03, dtrain, 10, watchlist,
-                            early_stopping_rounds=2)
-        gbdt_04 = xgb.train(self.xgb_params_04, dtrain, 10, watchlist,
-                            early_stopping_rounds=2)
+        gbdt_01 = xgb.train(
+            self.xgb_params_01, dtrain, 10, watchlist, early_stopping_rounds=2
+        )
+        gbdt_02 = xgb.train(
+            self.xgb_params_02, dtrain, 10, watchlist, early_stopping_rounds=2
+        )
+        gbdt_03 = xgb.train(
+            self.xgb_params_03, dtrain, 10, watchlist, early_stopping_rounds=2
+        )
+        gbdt_04 = xgb.train(
+            self.xgb_params_04, dtrain, 10, watchlist, early_stopping_rounds=2
+        )
         assert gbdt_01.predict(dvalid)[0] == gbdt_02.predict(dvalid)[0]
         assert gbdt_01.predict(dvalid)[0] == gbdt_03.predict(dvalid)[0]
         assert gbdt_03.predict(dvalid)[0] != gbdt_04.predict(dvalid)[0]
 
-        gbdt_01 = xgb.train(self.xgb_params_01, dtrain, 10, watchlist,
-                            early_stopping_rounds=2, feval=self.evalerror_01)
-        gbdt_02 = xgb.train(self.xgb_params_02, dtrain, 10, watchlist,
-                            early_stopping_rounds=2, feval=self.evalerror_02)
-        gbdt_03 = xgb.train(self.xgb_params_03, dtrain, 10, watchlist,
-                            early_stopping_rounds=2, feval=self.evalerror_03)
-        gbdt_04 = xgb.train(self.xgb_params_04, dtrain, 10, watchlist,
-                            early_stopping_rounds=2, feval=self.evalerror_04)
+        gbdt_01 = xgb.train(
+            self.xgb_params_01,
+            dtrain,
+            10,
+            watchlist,
+            early_stopping_rounds=2,
+            feval=self.evalerror_01,
+        )
+        gbdt_02 = xgb.train(
+            self.xgb_params_02,
+            dtrain,
+            10,
+            watchlist,
+            early_stopping_rounds=2,
+            feval=self.evalerror_02,
+        )
+        gbdt_03 = xgb.train(
+            self.xgb_params_03,
+            dtrain,
+            10,
+            watchlist,
+            early_stopping_rounds=2,
+            feval=self.evalerror_03,
+        )
+        gbdt_04 = xgb.train(
+            self.xgb_params_04,
+            dtrain,
+            10,
+            watchlist,
+            early_stopping_rounds=2,
+            feval=self.evalerror_04,
+        )
         assert gbdt_01.predict(dvalid)[0] == gbdt_02.predict(dvalid)[0]
         assert gbdt_01.predict(dvalid)[0] == gbdt_03.predict(dvalid)[0]
         assert gbdt_03.predict(dvalid)[0] != gbdt_04.predict(dvalid)[0]
@@ -93,6 +125,7 @@ def test_eval_metrics(self):
     @pytest.mark.skipif(**tm.no_sklearn())
     def test_gamma_deviance(self):
         from sklearn.metrics import mean_gamma_deviance
+
         rng = np.random.RandomState(1994)
         n_samples = 100
         n_features = 30
@@ -101,8 +134,13 @@ def test_gamma_deviance(self):
         y = rng.randn(n_samples)
         y = y - y.min() * 100
 
-        reg = xgb.XGBRegressor(tree_method="hist", objective="reg:gamma", n_estimators=10)
-        reg.fit(X, y, eval_metric="gamma-deviance")
+        reg = xgb.XGBRegressor(
+            tree_method="hist",
+            objective="reg:gamma",
+            n_estimators=10,
+            eval_metric="gamma-deviance",
+        )
+        reg.fit(X, y)
 
         booster = reg.get_booster()
         score = reg.predict(X)
@@ -113,16 +151,26 @@ def test_gamma_deviance(self):
     @pytest.mark.skipif(**tm.no_sklearn())
     def test_gamma_lik(self) -> None:
         import scipy.stats as stats
+
         rng = np.random.default_rng(1994)
         n_samples = 32
         n_features = 10
 
-        X = rng.normal(0, 1, size=n_samples * n_features).reshape((n_samples, n_features))
+        X = rng.normal(0, 1, size=n_samples * n_features).reshape(
+            (n_samples, n_features)
+        )
 
         alpha, loc, beta = 5.0, 11.1, 22
-        y = stats.gamma.rvs(alpha, loc=loc, scale=beta, size=n_samples, random_state=rng)
-        reg = xgb.XGBRegressor(tree_method="hist", objective="reg:gamma", n_estimators=64)
-        reg.fit(X, y, eval_metric="gamma-nloglik", eval_set=[(X, y)])
+        y = stats.gamma.rvs(
+            alpha, loc=loc, scale=beta, size=n_samples, random_state=rng
+        )
+        reg = xgb.XGBRegressor(
+            tree_method="hist",
+            objective="reg:gamma",
+            n_estimators=64,
+            eval_metric="gamma-nloglik",
+        )
+        reg.fit(X, y, eval_set=[(X, y)])
 
         score = reg.predict(X)
 
@@ -134,7 +182,7 @@ def test_gamma_lik(self) -> None:
         # XGBoost uses the canonical link function of gamma in evaluation function.
         # so \theta = - (1.0 / y)
         # dispersion is hardcoded as 1.0, so shape (a in scipy parameter) is also 1.0
-        beta = - (1.0 / (- (1.0 / y)))  # == y
+        beta = -(1.0 / (-(1.0 / y)))  # == y
         nloglik_stats = -stats.gamma.logpdf(score, a=1.0, scale=beta)
 
         np.testing.assert_allclose(nloglik, np.mean(nloglik_stats), rtol=1e-3)
@@ -153,7 +201,7 @@ def run_roc_auc_binary(self, tree_method, n_samples):
             n_features,
             n_informative=n_features,
             n_redundant=0,
-            random_state=rng
+            random_state=rng,
         )
         Xy = xgb.DMatrix(X, y)
         booster = xgb.train(
@@ -197,7 +245,7 @@ def run_roc_auc_multi(self, tree_method, n_samples, weighted):
             n_informative=n_features,
             n_redundant=0,
             n_classes=n_classes,
-            random_state=rng
+            random_state=rng,
         )
         if weighted:
             weights = rng.randn(n_samples)
@@ -242,20 +290,25 @@ def test_roc_auc_multi(self, n_samples, weighted):
     def run_pr_auc_binary(self, tree_method):
         from sklearn.datasets import make_classification
         from sklearn.metrics import auc, precision_recall_curve
+
         X, y = make_classification(128, 4, n_classes=2, random_state=1994)
-        clf = xgb.XGBClassifier(tree_method=tree_method, n_estimators=1)
-        clf.fit(X, y, eval_metric="aucpr", eval_set=[(X, y)])
+        clf = xgb.XGBClassifier(
+            tree_method=tree_method, n_estimators=1, eval_metric="aucpr"
+        )
+        clf.fit(X, y, eval_set=[(X, y)])
         evals_result = clf.evals_result()["validation_0"]["aucpr"][-1]
 
         y_score = clf.predict_proba(X)[:, 1]  # get the positive column
         precision, recall, _ = precision_recall_curve(y, y_score)
         prauc = auc(recall, precision)
-        # Interpolation results are slightly different from sklearn, but overall should be
-        # similar.
+        # Interpolation results are slightly different from sklearn, but overall should
+        # be similar.
         np.testing.assert_allclose(prauc, evals_result, rtol=1e-2)
 
-        clf = xgb.XGBClassifier(tree_method=tree_method, n_estimators=10)
-        clf.fit(X, y, eval_metric="aucpr", eval_set=[(X, y)])
+        clf = xgb.XGBClassifier(
+            tree_method=tree_method, n_estimators=10, eval_metric="aucpr"
+        )
+        clf.fit(X, y, eval_set=[(X, y)])
         evals_result = clf.evals_result()["validation_0"]["aucpr"][-1]
         np.testing.assert_allclose(0.99, evals_result, rtol=1e-2)
 
@@ -264,16 +317,21 @@ def test_pr_auc_binary(self):
 
     def run_pr_auc_multi(self, tree_method):
         from sklearn.datasets import make_classification
+
         X, y = make_classification(
             64, 16, n_informative=8, n_classes=3, random_state=1994
         )
-        clf = xgb.XGBClassifier(tree_method=tree_method, n_estimators=1)
-        clf.fit(X, y, eval_metric="aucpr", eval_set=[(X, y)])
+        clf = xgb.XGBClassifier(
+            tree_method=tree_method, n_estimators=1, eval_metric="aucpr"
+        )
+        clf.fit(X, y, eval_set=[(X, y)])
         evals_result = clf.evals_result()["validation_0"]["aucpr"][-1]
-        # No available implementation for comparison, just check that XGBoost converges to
-        # 1.0
-        clf = xgb.XGBClassifier(tree_method=tree_method, n_estimators=10)
-        clf.fit(X, y, eval_metric="aucpr", eval_set=[(X, y)])
+        # No available implementation for comparison, just check that XGBoost converges
+        # to 1.0
+        clf = xgb.XGBClassifier(
+            tree_method=tree_method, n_estimators=10, eval_metric="aucpr"
+        )
+        clf.fit(X, y, eval_set=[(X, y)])
         evals_result = clf.evals_result()["validation_0"]["aucpr"][-1]
         np.testing.assert_allclose(1.0, evals_result, rtol=1e-2)
 
@@ -282,9 +340,13 @@ def test_pr_auc_multi(self):
 
     def run_pr_auc_ltr(self, tree_method):
         from sklearn.datasets import make_classification
+
         X, y = make_classification(128, 4, n_classes=2, random_state=1994)
         ltr = xgb.XGBRanker(
-            tree_method=tree_method, n_estimators=16, objective="rank:pairwise"
+            tree_method=tree_method,
+            n_estimators=16,
+            objective="rank:pairwise",
+            eval_metric="aucpr",
         )
         groups = np.array([32, 32, 64])
         ltr.fit(
@@ -293,7 +355,6 @@ def run_pr_auc_ltr(self, tree_method):
             group=groups,
             eval_set=[(X, y)],
             eval_group=[groups],
-            eval_metric="aucpr",
         )
         results = ltr.evals_result()["validation_0"]["aucpr"]
         assert results[-1] >= 0.99
diff --git a/tests/python/test_training_continuation.py b/tests/python/test_training_continuation.py
index 6b2f9630136d..1798a4d932ff 100644
--- a/tests/python/test_training_continuation.py
+++ b/tests/python/test_training_continuation.py
@@ -149,8 +149,8 @@ def test_changed_parameter(self):
         from sklearn.datasets import load_breast_cancer
 
         X, y = load_breast_cancer(return_X_y=True)
-        clf = xgb.XGBClassifier(n_estimators=2)
-        clf.fit(X, y, eval_set=[(X, y)], eval_metric="logloss")
+        clf = xgb.XGBClassifier(n_estimators=2, eval_metric="logloss")
+        clf.fit(X, y, eval_set=[(X, y)])
         assert tm.non_increasing(clf.evals_result()["validation_0"]["logloss"])
 
         with tempfile.TemporaryDirectory() as tmpdir:
@@ -160,5 +160,6 @@ def test_changed_parameter(self):
 
         clf = xgb.XGBClassifier(n_estimators=2)
         # change metric to error
-        clf.fit(X, y, eval_set=[(X, y)], eval_metric="error")
+        clf.set_params(eval_metric="error")
+        clf.fit(X, y, eval_set=[(X, y)], xgb_model=loaded)
         assert tm.non_increasing(clf.evals_result()["validation_0"]["error"])
diff --git a/tests/python/test_with_sklearn.py b/tests/python/test_with_sklearn.py
index 47f1778d64e7..9047cee6e518 100644
--- a/tests/python/test_with_sklearn.py
+++ b/tests/python/test_with_sklearn.py
@@ -30,8 +30,8 @@ def test_binary_classification():
     kf = KFold(n_splits=2, shuffle=True, random_state=rng)
     for cls in (xgb.XGBClassifier, xgb.XGBRFClassifier):
         for train_index, test_index in kf.split(X, y):
-            clf = cls(random_state=42)
-            xgb_model = clf.fit(X[train_index], y[train_index], eval_metric=['auc', 'logloss'])
+            clf = cls(random_state=42, eval_metric=['auc', 'logloss'])
+            xgb_model = clf.fit(X[train_index], y[train_index])
             preds = xgb_model.predict(X[test_index])
             labels = y[test_index]
             err = sum(1 for i in range(len(preds))
@@ -101,10 +101,11 @@ def test_best_iteration():
     def train(booster: str, forest: Optional[int]) -> None:
         rounds = 4
         cls = xgb.XGBClassifier(
-            n_estimators=rounds, num_parallel_tree=forest, booster=booster
-        ).fit(
-            X, y, eval_set=[(X, y)], early_stopping_rounds=3
-        )
+            n_estimators=rounds,
+            num_parallel_tree=forest,
+            booster=booster,
+            early_stopping_rounds=3,
+        ).fit(X, y, eval_set=[(X, y)])
         assert cls.best_iteration == rounds - 1
 
         # best_iteration is used by default, assert that under gblinear it's
@@ -112,9 +113,9 @@ def train(booster: str, forest: Optional[int]) -> None:
         cls.predict(X)
 
     num_parallel_tree = 4
-    train('gbtree', num_parallel_tree)
-    train('dart', num_parallel_tree)
-    train('gblinear', None)
+    train("gbtree", num_parallel_tree)
+    train("dart", num_parallel_tree)
+    train("gblinear", None)
 
 
 def test_ranking():
@@ -258,6 +259,7 @@ def test_stacking_classification():
     X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=42)
     clf.fit(X_train, y_train).score(X_test, y_test)
 
+
 @pytest.mark.skipif(**tm.no_pandas())
 def test_feature_importances_weight():
     from sklearn.datasets import load_digits
@@ -474,7 +476,8 @@ def run_housing_rf_regression(tree_method):
 
     rfreg = xgb.XGBRFRegressor()
     with pytest.raises(NotImplementedError):
-        rfreg.fit(X, y, early_stopping_rounds=10)
+        rfreg.set_params(early_stopping_rounds=10)
+        rfreg.fit(X, y)
 
 
 def test_rf_regression():
@@ -574,7 +577,7 @@ def wrapped(y, p):
         return logregobj(y, p)
 
     cls.set_params(objective=wrapped)
-    cls.predict(X)              # no throw
+    cls.predict(X)  # no throw
     cls.fit(X, y)
 
     assert is_called[0]
@@ -844,51 +847,65 @@ def run_validation_weights(model):
     y_train, y_test = y[:1600], y[1600:]
 
     # instantiate model
-    param_dist = {'objective': 'binary:logistic', 'n_estimators': 2,
-                  'random_state': 123}
+    param_dist = {
+        "objective": "binary:logistic",
+        "n_estimators": 2,
+        "random_state": 123,
+    }
     clf = model(**param_dist)
 
     # train it using instance weights only in the training set
     weights_train = np.random.choice([1, 2], len(X_train))
-    clf.fit(X_train, y_train,
-            sample_weight=weights_train,
-            eval_set=[(X_test, y_test)],
-            eval_metric='logloss',
-            verbose=False)
-
+    clf.set_params(eval_metric="logloss")
+    clf.fit(
+        X_train,
+        y_train,
+        sample_weight=weights_train,
+        eval_set=[(X_test, y_test)],
+        verbose=False,
+    )
     # evaluate logloss metric on test set *without* using weights
     evals_result_without_weights = clf.evals_result()
-    logloss_without_weights = evals_result_without_weights[
-        "validation_0"]["logloss"]
+    logloss_without_weights = evals_result_without_weights["validation_0"]["logloss"]
 
     # now use weights for the test set
     np.random.seed(0)
     weights_test = np.random.choice([1, 2], len(X_test))
-    clf.fit(X_train, y_train,
-            sample_weight=weights_train,
-            eval_set=[(X_test, y_test)],
-            sample_weight_eval_set=[weights_test],
-            eval_metric='logloss',
-            verbose=False)
+    clf.set_params(eval_metric="logloss")
+    clf.fit(
+        X_train,
+        y_train,
+        sample_weight=weights_train,
+        eval_set=[(X_test, y_test)],
+        sample_weight_eval_set=[weights_test],
+        verbose=False,
+    )
     evals_result_with_weights = clf.evals_result()
     logloss_with_weights = evals_result_with_weights["validation_0"]["logloss"]
 
     # check that the logloss in the test set is actually different when using
     # weights than when not using them
-    assert all((logloss_with_weights[i] != logloss_without_weights[i]
-                for i in [0, 1]))
+    assert all((logloss_with_weights[i] != logloss_without_weights[i] for i in [0, 1]))
 
     with pytest.raises(ValueError):
         # length of eval set and sample weight doesn't match.
-        clf.fit(X_train, y_train, sample_weight=weights_train,
-                eval_set=[(X_train, y_train), (X_test, y_test)],
-                sample_weight_eval_set=[weights_train])
+        clf.fit(
+            X_train,
+            y_train,
+            sample_weight=weights_train,
+            eval_set=[(X_train, y_train), (X_test, y_test)],
+            sample_weight_eval_set=[weights_train],
+        )
 
     with pytest.raises(ValueError):
         cls = xgb.XGBClassifier()
-        cls.fit(X_train, y_train, sample_weight=weights_train,
-                eval_set=[(X_train, y_train), (X_test, y_test)],
-                sample_weight_eval_set=[weights_train])
+        cls.fit(
+            X_train,
+            y_train,
+            sample_weight=weights_train,
+            eval_set=[(X_train, y_train), (X_test, y_test)],
+            sample_weight_eval_set=[weights_train],
+        )
 
 
 def test_validation_weights():
@@ -960,8 +977,7 @@ def test_XGBClassifier_resume():
 
         # file name of stored xgb model
         model1.save_model(model1_path)
-        model2 = xgb.XGBClassifier(
-            learning_rate=0.3, random_state=0, n_estimators=8)
+        model2 = xgb.XGBClassifier(learning_rate=0.3, random_state=0, n_estimators=8)
         model2.fit(X, Y, xgb_model=model1_path)
 
         pred2 = model2.predict(X)
@@ -972,8 +988,7 @@ def test_XGBClassifier_resume():
 
         # file name of 'Booster' instance Xgb model
         model1.get_booster().save_model(model1_booster_path)
-        model2 = xgb.XGBClassifier(
-            learning_rate=0.3, random_state=0, n_estimators=8)
+        model2 = xgb.XGBClassifier(learning_rate=0.3, random_state=0, n_estimators=8)
         model2.fit(X, Y, xgb_model=model1_booster_path)
 
         pred2 = model2.predict(X)
@@ -1279,12 +1294,16 @@ def test_estimator_reg(estimator, check):
         ):
             estimator.fit(X, y)
         return
-    if os.environ["PYTEST_CURRENT_TEST"].find("check_estimators_overwrite_params") != -1:
+    if (
+        os.environ["PYTEST_CURRENT_TEST"].find("check_estimators_overwrite_params")
+        != -1
+    ):
         # A hack to pass the scikit-learn parameter mutation tests.  XGBoost regressor
-        # returns actual internal default values for parameters in `get_params`, but those
-        # are set as `None` in sklearn interface to avoid duplication.  So we fit a dummy
-        # model and obtain the default parameters here for the mutation tests.
+        # returns actual internal default values for parameters in `get_params`, but
+        # those are set as `None` in sklearn interface to avoid duplication.  So we fit
+        # a dummy model and obtain the default parameters here for the mutation tests.
         from sklearn.datasets import make_regression
+
         X, y = make_regression(n_samples=2, n_features=1)
         estimator.set_params(**xgb.XGBRegressor().fit(X, y).get_params())
 
@@ -1325,6 +1344,7 @@ def test_categorical():
 def test_evaluation_metric():
     from sklearn.datasets import load_diabetes, load_digits
     from sklearn.metrics import mean_absolute_error
+
     X, y = load_diabetes(return_X_y=True)
     n_estimators = 16
 
@@ -1341,17 +1361,6 @@ def test_evaluation_metric():
     for line in lines:
         assert line.find("mean_absolute_error") != -1
 
-    def metric(predt: np.ndarray, Xy: xgb.DMatrix):
-        y = Xy.get_label()
-        return "m", np.abs(predt - y).sum()
-
-    with pytest.warns(UserWarning):
-        reg = xgb.XGBRegressor(
-            tree_method="hist",
-            n_estimators=1,
-        )
-        reg.fit(X, y, eval_set=[(X, y)], eval_metric=metric)
-
     def merror(y_true: np.ndarray, predt: np.ndarray):
         n_samples = y_true.shape[0]
         assert n_samples == predt.size
diff --git a/tests/test_distributed/test_gpu_with_dask/test_gpu_with_dask.py b/tests/test_distributed/test_gpu_with_dask/test_gpu_with_dask.py
index a15e1903d238..865623671388 100644
--- a/tests/test_distributed/test_gpu_with_dask/test_gpu_with_dask.py
+++ b/tests/test_distributed/test_gpu_with_dask/test_gpu_with_dask.py
@@ -363,12 +363,12 @@ def test_early_stopping(self, local_cuda_client: Client) -> None:
             device="cuda",
             eval_metric="error",
             n_estimators=100,
+            early_stopping_rounds=early_stopping_rounds,
         )
         cls.client = local_cuda_client
         cls.fit(
             X,
             y,
-            early_stopping_rounds=early_stopping_rounds,
             eval_set=[(valid_X, valid_y)],
         )
         booster = cls.get_booster()
diff --git a/tests/test_distributed/test_with_dask/test_with_dask.py b/tests/test_distributed/test_with_dask/test_with_dask.py
index 79df025fead1..150e698d35c4 100644
--- a/tests/test_distributed/test_with_dask/test_with_dask.py
+++ b/tests/test_distributed/test_with_dask/test_with_dask.py
@@ -937,8 +937,10 @@ def run_empty_dmatrix_auc(client: "Client", device: str, n_workers: int) -> None
     valid_X = dd.from_array(valid_X_, chunksize=n_samples)
     valid_y = dd.from_array(valid_y_, chunksize=n_samples)
 
-    cls = xgb.dask.DaskXGBClassifier(device=device, n_estimators=2)
-    cls.fit(X, y, eval_metric=["auc", "aucpr"], eval_set=[(valid_X, valid_y)])
+    cls = xgb.dask.DaskXGBClassifier(
+        device=device, n_estimators=2, eval_metric=["auc", "aucpr"]
+    )
+    cls.fit(X, y, eval_set=[(valid_X, valid_y)])
 
     # multiclass
     X_, y_ = make_classification(
@@ -966,8 +968,10 @@ def run_empty_dmatrix_auc(client: "Client", device: str, n_workers: int) -> None
     valid_X = dd.from_array(valid_X_, chunksize=n_samples)
     valid_y = dd.from_array(valid_y_, chunksize=n_samples)
 
-    cls = xgb.dask.DaskXGBClassifier(device=device, n_estimators=2)
-    cls.fit(X, y, eval_metric=["auc", "aucpr"], eval_set=[(valid_X, valid_y)])
+    cls = xgb.dask.DaskXGBClassifier(
+        device=device, n_estimators=2, eval_metric=["auc", "aucpr"]
+    )
+    cls.fit(X, y, eval_set=[(valid_X, valid_y)])
 
 
 def test_empty_dmatrix_auc() -> None:
@@ -994,11 +998,11 @@ def run_auc(client: "Client", device: str) -> None:
     valid_X = dd.from_array(valid_X_, chunksize=10)
     valid_y = dd.from_array(valid_y_, chunksize=10)
 
-    cls = xgb.XGBClassifier(device=device, n_estimators=2)
-    cls.fit(X_, y_, eval_metric="auc", eval_set=[(valid_X_, valid_y_)])
+    cls = xgb.XGBClassifier(device=device, n_estimators=2, eval_metric="auc")
+    cls.fit(X_, y_, eval_set=[(valid_X_, valid_y_)])
 
-    dcls = xgb.dask.DaskXGBClassifier(device=device, n_estimators=2)
-    dcls.fit(X, y, eval_metric="auc", eval_set=[(valid_X, valid_y)])
+    dcls = xgb.dask.DaskXGBClassifier(device=device, n_estimators=2, eval_metric="auc")
+    dcls.fit(X, y, eval_set=[(valid_X, valid_y)])
 
     approx = dcls.evals_result()["validation_0"]["auc"]
     exact = cls.evals_result()["validation_0"]["auc"]
@@ -1267,16 +1271,16 @@ def test_dask_ranking(client: "Client") -> None:
     qid_valid = qid_valid.astype(np.uint32)
     qid_test = qid_test.astype(np.uint32)
 
-    rank = xgb.dask.DaskXGBRanker(n_estimators=2500)
+    rank = xgb.dask.DaskXGBRanker(
+        n_estimators=2500, eval_metric=["ndcg"], early_stopping_rounds=10
+    )
     rank.fit(
         x_train,
         y_train,
         qid=qid_train,
         eval_set=[(x_test, y_test), (x_train, y_train)],
         eval_qid=[qid_test, qid_train],
-        eval_metric=["ndcg"],
         verbose=True,
-        early_stopping_rounds=10,
     )
     assert rank.n_features_in_ == 46
     assert rank.best_score > 0.98
@@ -2150,13 +2154,15 @@ def test_early_stopping(self, client: "Client") -> None:
         valid_X, valid_y = load_breast_cancer(return_X_y=True)
         valid_X, valid_y = da.from_array(valid_X), da.from_array(valid_y)
         cls = xgb.dask.DaskXGBClassifier(
-            objective="binary:logistic", tree_method="hist", n_estimators=1000
+            objective="binary:logistic",
+            tree_method="hist",
+            n_estimators=1000,
+            early_stopping_rounds=early_stopping_rounds,
         )
         cls.client = client
         cls.fit(
             X,
             y,
-            early_stopping_rounds=early_stopping_rounds,
             eval_set=[(valid_X, valid_y)],
         )
         booster = cls.get_booster()
@@ -2165,15 +2171,17 @@ def test_early_stopping(self, client: "Client") -> None:
 
         # Specify the metric
         cls = xgb.dask.DaskXGBClassifier(
-            objective="binary:logistic", tree_method="hist", n_estimators=1000
+            objective="binary:logistic",
+            tree_method="hist",
+            n_estimators=1000,
+            early_stopping_rounds=early_stopping_rounds,
+            eval_metric="error",
         )
         cls.client = client
         cls.fit(
             X,
             y,
-            early_stopping_rounds=early_stopping_rounds,
             eval_set=[(valid_X, valid_y)],
-            eval_metric="error",
         )
         assert tm.non_increasing(cls.evals_result()["validation_0"]["error"])
         booster = cls.get_booster()
@@ -2215,12 +2223,12 @@ def test_early_stopping_custom_eval(self, client: "Client") -> None:
             tree_method="hist",
             n_estimators=1000,
             eval_metric=tm.eval_error_metric_skl,
+            early_stopping_rounds=early_stopping_rounds,
         )
         cls.client = client
         cls.fit(
             X,
             y,
-            early_stopping_rounds=early_stopping_rounds,
             eval_set=[(valid_X, valid_y)],
         )
         booster = cls.get_booster()
@@ -2234,21 +2242,22 @@ def test_callback(self, client: "Client") -> None:
         X, y = load_breast_cancer(return_X_y=True)
         X, y = da.from_array(X), da.from_array(y)
 
-        cls = xgb.dask.DaskXGBClassifier(
-            objective="binary:logistic", tree_method="hist", n_estimators=10
-        )
-        cls.client = client
-
         with tempfile.TemporaryDirectory() as tmpdir:
-            cls.fit(
-                X,
-                y,
+            cls = xgb.dask.DaskXGBClassifier(
+                objective="binary:logistic",
+                tree_method="hist",
+                n_estimators=10,
                 callbacks=[
                     xgb.callback.TrainingCheckPoint(
                         directory=Path(tmpdir), interval=1, name="model"
                     )
                 ],
             )
+            cls.client = client
+            cls.fit(
+                X,
+                y,
+            )
             for i in range(1, 10):
                 assert os.path.exists(
                     os.path.join(
diff --git a/tests/test_distributed/test_with_spark/test_spark_local.py b/tests/test_distributed/test_with_spark/test_spark_local.py
index 406174542416..b8c16ef1cd05 100644
--- a/tests/test_distributed/test_with_spark/test_spark_local.py
+++ b/tests/test_distributed/test_with_spark/test_spark_local.py
@@ -311,24 +311,20 @@ def clf_with_weight(
     y_val = np.array([0, 1])
     w_train = np.array([1.0, 2.0])
     w_val = np.array([1.0, 2.0])
-    cls2 = XGBClassifier()
+    cls2 = XGBClassifier(eval_metric="logloss", early_stopping_rounds=1)
     cls2.fit(
         X_train,
         y_train,
         eval_set=[(X_val, y_val)],
-        early_stopping_rounds=1,
-        eval_metric="logloss",
     )
 
-    cls3 = XGBClassifier()
+    cls3 = XGBClassifier(eval_metric="logloss", early_stopping_rounds=1)
     cls3.fit(
         X_train,
         y_train,
         sample_weight=w_train,
         eval_set=[(X_val, y_val)],
         sample_weight_eval_set=[w_val],
-        early_stopping_rounds=1,
-        eval_metric="logloss",
     )
 
     cls_df_train_with_eval_weight = spark.createDataFrame(