[`gpt2-int8`] Add gpt2-xl int8 test (#24543)

add gpt2-xl test

tests/bnb/test_mixed_int8.py

@@ -762,8 +762,24 @@ class MixedInt8TestTraining(BaseMixedInt8Test):
 class MixedInt8GPT2Test(MixedInt8Test):
     model_name = "gpt2-xl"
     EXPECTED_RELATIVE_DIFFERENCE = 1.8720077507258357
-    EXPECTED_OUTPUT = "Hello my name is John Doe, and I am a member of the"
+    EXPECTED_OUTPUT = "Hello my name is John Doe, and I'm a big fan of"
 
     def test_int8_from_pretrained(self):
-        # TODO @younesbelkada: Test loading quantized gpt2 model from the hub.
-        pass
+        r"""
+        Test whether loading a 8bit model from the Hub works as expected
+        """
+        from bitsandbytes.nn import Int8Params
+
+        model_id = "ybelkada/gpt2-xl-8bit"
+
+        model = AutoModelForCausalLM.from_pretrained(model_id)
+
+        linear = get_some_linear_layer(model)
+        self.assertTrue(linear.weight.__class__ == Int8Params)
+        self.assertTrue(hasattr(linear.weight, "SCB"))
+
+        # generate
+        encoded_input = self.tokenizer(self.input_text, return_tensors="pt")
+        output_sequences = model.generate(input_ids=encoded_input["input_ids"].to(0), max_new_tokens=10)
+
+        self.assertEqual(self.tokenizer.decode(output_sequences[0], skip_special_tokens=True), self.EXPECTED_OUTPUT)