Add capteesys capture fixture to bubble up output to --capture handler

doc/en/how-to/capture-stdout-stderr.rst

@@ -4,6 +4,15 @@
 How to capture stdout/stderr output
 =========================================================
 
+Pytest can intercept stdout and stderr. Using the `--capture=` command-line
+argument (described below) allows pytest to add captured output to reports
+generated after tests. The reports can customized by `-r` (described below).
+
+Built-in fixtures (also described below) can be passed to tests as arguments
+to capture stdout and stderr and make it accessible to the developer during
+the test for inspection. It will not be available for reports if it is captured,
+unless it is re-printed with capturing turned off (see below).
+
 Default stdout/stderr/stdin capturing behaviour
 ---------------------------------------------------------
 
@@ -106,8 +115,8 @@ of the failing function and hide the other one:
 Accessing captured output from a test function
 ---------------------------------------------------
 
-The :fixture:`capsys`, :fixture:`capsysbinary`, :fixture:`capfd`, and :fixture:`capfdbinary` fixtures
-allow access to ``stdout``/``stderr`` output created during test execution.
+The :fixture:`capsys`, :fixture:`capteesys`, :fixture:`capsysbinary`, :fixture:`capfd`, and :fixture:`capfdbinary`
+fixtures allow access to ``stdout``/``stderr`` output created during test execution.
 
 Here is an example test function that performs some output related checks:
 

src/_pytest/capture.py

@@ -902,11 +902,13 @@ def __init__(
         captureclass: type[CaptureBase[AnyStr]],
         request: SubRequest,
         *,
+        config: dict[str, Any] | None = None,
         _ispytest: bool = False,
     ) -> None:
         check_ispytest(_ispytest)
         self.captureclass: type[CaptureBase[AnyStr]] = captureclass
         self.request = request
+        self._config = config if config else {}
         self._capture: MultiCapture[AnyStr] | None = None
         self._captured_out: AnyStr = self.captureclass.EMPTY_BUFFER
         self._captured_err: AnyStr = self.captureclass.EMPTY_BUFFER
@@ -915,8 +917,8 @@ def _start(self) -> None:
         if self._capture is None:
             self._capture = MultiCapture(
                 in_=None,
-                out=self.captureclass(1),
-                err=self.captureclass(2),
+                out=self.captureclass(1, **self._config),
+                err=self.captureclass(2, **self._config),
             )
             self._capture.start_capturing()
 
@@ -1002,6 +1004,40 @@ def test_output(capsys):
     capman.unset_fixture()
 
 
+@fixture
+def capteesys(request: SubRequest) -> Generator[CaptureFixture[str]]:
+    r"""Enable simultaneous text capturing and pass-through of writes
+    to ``sys.stdout`` and ``sys.stderr``.
+
+
+    The captured output is made available via ``capteesys.readouterr()`` method
+    calls, which return a ``(out, err)`` namedtuple.
+    ``out`` and ``err`` will be ``text`` objects.
+
+    The output is also passed-through, allowing it to be "live-printed".
+
+    Returns an instance of :class:`CaptureFixture[str] <pytest.CaptureFixture>`.
+
+    Example:
+
+    .. code-block:: python
+
+        def test_output(capsys):
+            print("hello")
+            captured = capteesys.readouterr()
+            assert captured.out == "hello\n"
+    """
+    capman: CaptureManager = request.config.pluginmanager.getplugin("capturemanager")
+    capture_fixture = CaptureFixture(
+        SysCapture, request, config=dict(tee=True), _ispytest=True
+    )
+    capman.set_fixture(capture_fixture)
+    capture_fixture._start()
+    yield capture_fixture
+    capture_fixture.close()
+    capman.unset_fixture()
+
+
 @fixture
 def capsysbinary(request: SubRequest) -> Generator[CaptureFixture[bytes]]:
     r"""Enable bytes capturing of writes to ``sys.stdout`` and ``sys.stderr``.