VLMs: fix number of image tokens (#34332)

* fix

* fix tests

* add tests

* style

* style

* fix qwen after rebase

* fix video llava

tests/models/llava/test_modeling_llava.py

@@ -235,6 +235,35 @@ class LlavaForConditionalGenerationModelTest(ModelTesterMixin, GenerationTesterM
                 out_embeds = model(inputs_embeds=inputs_embeds, **inputs)[0]
             self.assertTrue(torch.allclose(out_embeds, out_ids))
 
+    def test_mismatching_num_image_tokens(self):
+        """
+        Tests that VLMs through an error with explicit message saying what is wrong
+        when number of images don't match number of image tokens in the text.
+        Also we need to test multi-image cases when one prompr has multiple image tokens.
+        """
+        config, input_dict = self.model_tester.prepare_config_and_inputs_for_common()
+        for model_class in self.all_model_classes:
+            model = model_class(config).to(torch_device)
+            _ = model(**input_dict)  # successfull forward with no modifications
+
+            # remove one image but leave the image token in text
+            input_dict["pixel_values"] = input_dict["pixel_values"][-1:, ...]
+            with self.assertRaises(ValueError):
+                _ = model(**input_dict)
+
+            # simulate multi-image case by concatenating inputs where each has exactly one image/image-token
+            input_ids = input_dict["input_ids"][:1]
+            pixel_values = input_dict["pixel_values"][:1]
+            input_ids = torch.cat([input_ids, input_ids], dim=0)
+
+            # one image and two image tokens raise an error
+            with self.assertRaises(ValueError):
+                _ = model(input_ids=input_ids, pixel_values=pixel_values)
+
+            # two images and two image tokens don't raise an error
+            pixel_values = torch.cat([pixel_values, pixel_values], dim=0)
+            _ = model(input_ids=input_ids, pixel_values=pixel_values)
+
     @unittest.skip(
         reason="This architecure seem to not compute gradients properly when using GC, check: https://github.com/huggingface/transformers/pull/27124"
     )