[processors] add tests for helper fn (#39629)

* add tests for helpers

* duplicate test for each model

* why llava next video has no helper

* oops must have been in the commit

* fix test after rebase

* add copy from

tests/models/gemma3/test_processing_gemma3.py

@@ -58,6 +58,19 @@ class Gemma3ProcessorTest(ProcessorTesterMixin, unittest.TestCase):
         processor.save_pretrained(cls.tmpdirname)
         cls.image_token = processor.boi_token
 
+    # Copied from tests.models.llava.test_processor_llava.LlavaProcessorTest.test_get_num_vision_tokens
+    def test_get_num_vision_tokens(self):
+        "Tests general functionality of the helper used internally in vLLM"
+
+        processor = self.get_processor()
+
+        output = processor._get_num_multimodal_tokens(image_sizes=[(100, 100), (300, 100), (500, 30)])
+        self.assertTrue("num_image_tokens" in output)
+        self.assertEqual(len(output["num_image_tokens"]), 3)
+
+        self.assertTrue("num_image_patches" in output)
+        self.assertEqual(len(output["num_image_patches"]), 3)
+
     @classmethod
     def tearDownClass(cls):
         shutil.rmtree(cls.tmpdirname, ignore_errors=True)