Backbone add mixin tests (#22542)

* Add out_indices to backbones, deprecate out_features

* Update - can specify both out_features and out_indices but not both

* Add backbone mixin tests

* Test tidy up

* Add test_backbone for convnext

* Remove redefinition of method

* Update for Dinat and Nat backbones

* Update tests

* Smarter indexing

* Add checks on config creation for backbone

* PR comments

tests/models/convnext/test_modeling_convnext.py

@@ -22,6 +22,7 @@ from transformers import ConvNextConfig
 from transformers.testing_utils import require_torch, require_vision, slow, torch_device
 from transformers.utils import cached_property, is_torch_available, is_vision_available
 
+from ...test_backbone_common import BackboneTesterMixin
 from ...test_configuration_common import ConfigTester
 from ...test_modeling_common import ModelTesterMixin, floats_tensor, ids_tensor
 from ...test_pipeline_mixin import PipelineTesterMixin
@@ -57,6 +58,7 @@ class ConvNextModelTester:
         num_labels=10,
         initializer_range=0.02,
         out_features=["stage2", "stage3", "stage4"],
+        out_indices=[2, 3, 4],
         scope=None,
     ):
         self.parent = parent
@@ -73,6 +75,7 @@ class ConvNextModelTester:
         self.num_labels = num_labels
         self.initializer_range = initializer_range
         self.out_features = out_features
+        self.out_indices = out_indices
         self.scope = scope
 
     def prepare_config_and_inputs(self):
@@ -95,6 +98,7 @@ class ConvNextModelTester:
             is_decoder=False,
             initializer_range=self.initializer_range,
             out_features=self.out_features,
+            out_indices=self.out_indices,
             num_labels=self.num_labels,
         )
 
@@ -224,6 +228,10 @@ class ConvNextModelTest(ModelTesterMixin, PipelineTesterMixin, unittest.TestCase
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_model(*config_and_inputs)
 
+    def test_backbone(self):
+        config_and_inputs = self.model_tester.prepare_config_and_inputs()
+        self.model_tester.create_and_check_backbone(*config_and_inputs)
+
     def test_hidden_states_output(self):
         def check_hidden_states_output(inputs_dict, config, model_class):
             model = model_class(config)
@@ -299,3 +307,14 @@ class ConvNextModelIntegrationTest(unittest.TestCase):
         expected_slice = torch.tensor([-0.0260, -0.4739, 0.1911]).to(torch_device)
 
         self.assertTrue(torch.allclose(outputs.logits[0, :3], expected_slice, atol=1e-4))
+
+
+@require_torch
+class ConvNextBackboneTest(unittest.TestCase, BackboneTesterMixin):
+    all_model_classes = (ConvNextBackbone,) if is_torch_available() else ()
+    config_class = ConvNextConfig
+
+    has_attentions = False
+
+    def setUp(self):
+        self.model_tester = ConvNextModelTester(self)