diff --git a/tests/test_layers.py b/tests/test_layers.py
index 92f6b683d3..2cc8420abf 100644
--- a/tests/test_layers.py
+++ b/tests/test_layers.py
@@ -1,7 +1,7 @@
 import torch
 import torch.nn as nn
 
-from timm.layers import create_act_layer, set_layer_config
+from timm.layers import create_act_layer, set_layer_config, get_act_layer, get_act_fn
 
 import importlib
 import os
@@ -76,3 +76,46 @@ def test_hard_swish_grad():
 def test_hard_mish_grad():
     for _ in range(100):
         _run_act_layer_grad('hard_mish')
+
+def test_get_act_layer_empty_string():
+    # Empty string should return None
+    assert get_act_layer('') is None
+
+
+def test_create_act_layer_inplace_error():
+    class NoInplaceAct(nn.Module):
+        def __init__(self):
+            super().__init__()
+        def forward(self, x):
+            return x
+    
+    # Should recover when inplace arg causes TypeError
+    layer = create_act_layer(NoInplaceAct, inplace=True)
+    assert isinstance(layer, NoInplaceAct)
+
+
+def test_create_act_layer_edge_cases():
+    # Test None input
+    assert create_act_layer(None) is None
+    
+    # Test TypeError handling for inplace
+    class CustomAct(nn.Module):
+        def __init__(self, **kwargs):
+            super().__init__()
+        def forward(self, x):
+            return x
+            
+    result = create_act_layer(CustomAct, inplace=True)
+    assert isinstance(result, CustomAct)
+
+
+def test_get_act_fn_callable():
+    def custom_act(x): 
+        return x
+    assert get_act_fn(custom_act) is custom_act
+
+
+def test_get_act_fn_none():
+    assert get_act_fn(None) is None
+    assert get_act_fn('') is None
+
diff --git a/tests/test_optim.py b/tests/test_optim.py
index 38f625fb42..66aaadbf95 100644
--- a/tests/test_optim.py
+++ b/tests/test_optim.py
@@ -11,6 +11,8 @@
 import torch
 from torch.testing._internal.common_utils import TestCase
 from torch.nn import Parameter
+
+from timm.optim.optim_factory import param_groups_layer_decay, param_groups_weight_decay
 from timm.scheduler import PlateauLRScheduler
 
 from timm.optim import create_optimizer_v2
@@ -741,3 +743,82 @@ def test_lookahead_radam(optimizer):
         lambda params: create_optimizer_v2(params, optimizer, lr=1e-4)
     )
 
+
+def test_param_groups_layer_decay_with_end_decay():
+    model = torch.nn.Sequential(
+        torch.nn.Linear(10, 5),
+        torch.nn.ReLU(),
+        torch.nn.Linear(5, 2)
+    )
+    
+    param_groups = param_groups_layer_decay(
+        model,
+        weight_decay=0.05,
+        layer_decay=0.75,
+        end_layer_decay=0.5,
+        verbose=True
+    )
+    
+    assert len(param_groups) > 0
+    # Verify layer scaling is applied with end decay
+    for group in param_groups:
+        assert 'lr_scale' in group
+        assert group['lr_scale'] <= 1.0
+        assert group['lr_scale'] >= 0.5
+
+
+def test_param_groups_layer_decay_with_matcher():
+    class ModelWithMatcher(torch.nn.Module):
+        def __init__(self):
+            super().__init__()
+            self.layer1 = torch.nn.Linear(10, 5)
+            self.layer2 = torch.nn.Linear(5, 2)
+            
+        def group_matcher(self, coarse=False):
+            return lambda name: int(name.split('.')[0][-1])
+            
+    model = ModelWithMatcher()
+    param_groups = param_groups_layer_decay(
+        model,
+        weight_decay=0.05,
+        layer_decay=0.75,
+        verbose=True
+    )
+    
+    assert len(param_groups) > 0
+    # Verify layer scaling is applied
+    for group in param_groups:
+        assert 'lr_scale' in group
+        assert 'weight_decay' in group
+        assert len(group['params']) > 0
+
+
+def test_param_groups_weight_decay():
+    model = torch.nn.Sequential(
+        torch.nn.Linear(10, 5),
+        torch.nn.ReLU(),
+        torch.nn.Linear(5, 2)
+    )
+    weight_decay = 0.01
+    no_weight_decay_list = ['1.weight']
+    
+    param_groups = param_groups_weight_decay(
+        model, 
+        weight_decay=weight_decay,
+        no_weight_decay_list=no_weight_decay_list
+    )
+    
+    assert len(param_groups) == 2
+    assert param_groups[0]['weight_decay'] == 0.0
+    assert param_groups[1]['weight_decay'] == weight_decay
+    
+    # Verify parameters are correctly grouped
+    no_decay_params = set(param_groups[0]['params'])
+    decay_params = set(param_groups[1]['params'])
+    
+    for name, param in model.named_parameters():
+        if param.ndim <= 1 or name.endswith(".bias") or name in no_weight_decay_list:
+            assert param in no_decay_params
+        else:
+            assert param in decay_params
+
diff --git a/tests/test_utils.py b/tests/test_utils.py
index b0f890d2fe..1e2126eead 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -2,8 +2,15 @@
 from torchvision.ops.misc import FrozenBatchNorm2d
 
 import timm
+import pytest
 from timm.utils.model import freeze, unfreeze
+from timm.utils.model import ActivationStatsHook
+from timm.utils.model import extract_spp_stats
 
+from timm.utils.model import _freeze_unfreeze
+from timm.utils.model import avg_sq_ch_mean, avg_ch_var, avg_ch_var_residual
+from timm.utils.model import reparameterize_model
+from timm.utils.model import get_state_dict
 
 def test_freeze_unfreeze():
     model = timm.create_model('resnet18')
@@ -54,4 +61,132 @@ def test_freeze_unfreeze():
     freeze(model.layer1[0], ['bn1'])
     assert isinstance(model.layer1[0].bn1, FrozenBatchNorm2d)    
     unfreeze(model.layer1[0], ['bn1'])
-    assert isinstance(model.layer1[0].bn1, BatchNorm2d)
\ No newline at end of file
+    assert isinstance(model.layer1[0].bn1, BatchNorm2d)
+
+def test_activation_stats_hook_validation():
+    model = timm.create_model('resnet18')
+    
+    def test_hook(model, input, output):
+        return output.mean().item()
+    
+    # Test error case with mismatched lengths
+    with pytest.raises(ValueError, match="Please provide `hook_fns` for each `hook_fn_locs`"):
+        ActivationStatsHook(
+            model,
+            hook_fn_locs=['layer1.0.conv1', 'layer1.0.conv2'],
+            hook_fns=[test_hook]
+        )
+
+
+def test_extract_spp_stats():
+    model = timm.create_model('resnet18')
+    
+    def test_hook(model, input, output):
+        return output.mean().item()
+    
+    stats = extract_spp_stats(
+        model,
+        hook_fn_locs=['layer1.0.conv1'],
+        hook_fns=[test_hook],
+        input_shape=[2, 3, 32, 32]
+    )
+    
+    assert isinstance(stats, dict)
+    assert test_hook.__name__ in stats
+    assert isinstance(stats[test_hook.__name__], list)
+    assert len(stats[test_hook.__name__]) > 0
+
+def test_freeze_unfreeze_bn_root():
+    import torch.nn as nn
+    from timm.layers import BatchNormAct2d
+    
+    # Create batch norm layers
+    bn = nn.BatchNorm2d(10)
+    bn_act = BatchNormAct2d(10)
+    
+    # Test with BatchNorm2d as root
+    with pytest.raises(AssertionError):
+        _freeze_unfreeze(bn, mode="freeze")
+    
+    # Test with BatchNormAct2d as root
+    with pytest.raises(AssertionError):
+        _freeze_unfreeze(bn_act, mode="freeze")
+
+
+def test_activation_stats_functions():
+    import torch
+    
+    # Create sample input tensor [batch, channels, height, width]
+    x = torch.randn(2, 3, 4, 4)
+    
+    # Test avg_sq_ch_mean
+    result1 = avg_sq_ch_mean(None, None, x)
+    assert isinstance(result1, float)
+    
+    # Test avg_ch_var
+    result2 = avg_ch_var(None, None, x)
+    assert isinstance(result2, float)
+    
+    # Test avg_ch_var_residual
+    result3 = avg_ch_var_residual(None, None, x)
+    assert isinstance(result3, float)
+
+
+def test_reparameterize_model():
+    import torch.nn as nn
+    
+    class FusableModule(nn.Module):
+        def __init__(self):
+            super().__init__()
+            self.conv = nn.Conv2d(3, 3, 1)
+        
+        def fuse(self):
+            return nn.Identity()
+    
+    class ModelWithFusable(nn.Module):
+        def __init__(self):
+            super().__init__()
+            self.fusable = FusableModule()
+            self.normal = nn.Linear(10, 10)
+    
+    model = ModelWithFusable()
+    
+    # Test with inplace=False (should create a copy)
+    new_model = reparameterize_model(model, inplace=False)
+    assert isinstance(new_model.fusable, nn.Identity)
+    assert isinstance(model.fusable, FusableModule)  # Original unchanged
+    
+    # Test with inplace=True
+    reparameterize_model(model, inplace=True)
+    assert isinstance(model.fusable, nn.Identity)
+
+
+def test_get_state_dict_custom_unwrap():
+    import torch.nn as nn
+    
+    class CustomModel(nn.Module):
+        def __init__(self):
+            super().__init__()
+            self.linear = nn.Linear(10, 10)
+    
+    model = CustomModel()
+    
+    def custom_unwrap(m):
+        return m
+    
+    state_dict = get_state_dict(model, unwrap_fn=custom_unwrap)
+    assert 'linear.weight' in state_dict
+    assert 'linear.bias' in state_dict
+
+
+def test_freeze_unfreeze_string_input():
+    model = timm.create_model('resnet18')
+    
+    # Test with string input
+    _freeze_unfreeze(model, 'layer1', mode='freeze')
+    assert model.layer1[0].conv1.weight.requires_grad == False
+    
+    # Test unfreezing with string input
+    _freeze_unfreeze(model, 'layer1', mode='unfreeze')
+    assert model.layer1[0].conv1.weight.requires_grad == True
+