add test scanner (#39419)

* add test scanner

* add doc + license

* refactor for only 1 tree traversal

* add back test of only one method

* document single method scan

* format

* fixup generate tests

* minor fix

* fixup

* fixup doc

docs/source/en/internal/model_debugging_utils.md

@@ -247,3 +247,114 @@ first and last layer will be shown. This is useful when some layers (typically c
 layers.
 
 [[autodoc]] model_addition_debugger_context
+
+## Analyzer of skipped tests
+
+### Scan skipped tests - for model adders and maintainers
+
+This small util is a power user tool intended for model adders and maintainers. It lists all test methods
+existing in `test_modeling_common.py`, inherited by all model tester classes, and scans the repository to measure
+how many tests are being skipped and for which models. 
+
+### Rationale
+
+When porting models to transformers, tests fail as they should, and sometimes `test_modeling_common` feels irreconcilable with the peculiarities of our brand new model. But how can we be sure we're not breaking everything by adding a seemingly innocent skip?
+
+This utility:
+- scans all test_modeling_common methods
+- looks for times where a method is skipped
+- returns a summary json you can load as a DataFrame/inspect
+
+**For instance test_inputs_embeds is skipped in a whooping 39% proportion at the time of writing this util.**
+
+![download-icon](https://huggingface.co/datasets/huggingface/documentation-images/resolve/f7f671f69b88ce4967e19179172c248958d35742/transformers/tests_skipped_visualisation.png)
+
+
+### Usage 
+
+You can run the skipped test analyzer in two ways:
+
+#### Full scan (default)
+
+From the root of `transformers` repo, scans all common test methods and outputs the results to a JSON file (default: `all_tests_scan_result.json`).
+
+```bash
+python utils/scan_skipped_tests.py --output_dir path/to/output
+```
+
+- `--output_dir` (optional): Directory where the JSON results will be saved. Defaults to the current directory.
+
+**Example output:**
+
+```
+🔬 Parsing 331 model test files once each...
+📝 Aggregating 224 tests...
+  (224/224) test_update_candidate_strategy_with_matches_1es_3d_is_nonecodet_schedule_fa_kwargs
+✅ Scan complete.
+
+📄 JSON saved to /home/pablo/git/transformers/all_tests_scan_result.json
+
+```
+
+And it will generate `all_tests_scan_result.json` file that you can inspect. The JSON is indexed by method name, and each entry follows this schema, indicating the origin as well (from `common`or `GenerationMixin`.)
+
+```json
+{
+  "<method_name>": {
+    "origin": "<test suite>"
+    "models_ran": ["<model_name>", ...],
+    "models_skipped": ["<model_name>", ...],
+    "skipped_proportion": <float>,
+    "reasons_skipped": ["<model_name>: <reason>",
+      ...
+    ]
+  },
+  ...
+}
+```
+
+Which you can visualise as above with e.g. `pandas`
+
+```python
+df = pd.read_json('all_tests_scan_result.json').T
+df.sort_values(by=['skipped_proportion'], ascending=False)
+
+```
+
+### Scan a single test method
+
+You can focus on a specific test method using `--test_method_name`:
+
+```bash
+$ python utils/scan_skipped_tests.py --test_method_name test_inputs_embeds --output_dir path/to/output
+```
+
+- `--test_method_name`: Name of the test method to scan (e.g., `test_inputs_embeds`).
+- `--output_dir` (optional): Directory where the JSON result will be saved.
+
+**Example output:**
+
+```bash
+$ python utils/scan_skipped_tests.py --test_method_name test_inputs_embeds
+
+🔬 Parsing 331 model test files once each...
+
+== test_inputs_embeds ==
+
+Ran    : 199/323
+Skipped : 124/323 (38.4%)
+ - aimv2: Aimv2 does not use inputs_embeds
+ - align: Inputs_embeds is tested in individual model tests
+ - altclip: Inputs_embeds is tested in individual model tests
+ - audio_spectrogram_transformer: AST does not use inputs_embeds
+ - beit: BEiT does not use inputs_embeds
+ - bit: Bit does not use inputs_embeds
+ - blip: Blip does not use inputs_embeds
+ - blip_2: Inputs_embeds is tested in individual model tests
+ - bridgetower: 
+ - canine: CANINE does not have a get_input_embeddings() method.
+ - ...
+
+📄 JSON saved to /home/pablo/git/transformers/scan_test_inputs_embeds.json
+
+```