[ProphetNet] Add Question Generation Model + Test (#7942)

* new prophetnet model

* correct name

* make style

tests/test_modeling_prophetnet.py

@@ -1073,3 +1073,33 @@ class ProphetNetModelIntegrationTest(unittest.TestCase):
             [EXPECTED_SUMMARIZE_100],
             generated_titles,
         )
+
+    @slow
+    def test_question_gen_inference(self):
+        model = ProphetNetForConditionalGeneration.from_pretrained("microsoft/prophetnet-large-uncased-squad-qg")
+        model.to(torch_device)
+
+        tokenizer = ProphetNetTokenizer.from_pretrained("microsoft/prophetnet-large-uncased-squad-qg")
+
+        INPUTS = [
+            "Bill Gates [SEP] Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975.",
+            "1975 [SEP] Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975.",
+            "April 4, 1975 [SEP] Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975.",
+        ]
+
+        input_ids = tokenizer(INPUTS, truncation=True, padding=True, return_tensors="pt").input_ids
+        input_ids = input_ids.to(torch_device)
+
+        gen_output = model.generate(input_ids, num_beams=5, early_stopping=True)
+        generated_questions = tokenizer.batch_decode(gen_output, skip_special_tokens=True)
+
+        EXPECTED_QUESTIONS = [
+            "along with paul allen, who founded microsoft?",
+            "what year was microsoft founded?",
+            "on what date was microsoft founded?",
+        ]
+
+        self.assertListEqual(
+            EXPECTED_QUESTIONS,
+            generated_questions,
+        )