Raise relevent err when wrong type is passed in as the accelerator_config (#29997)

* Raise relevent err

* Use type instead

tests/trainer/test_trainer.py

@@ -3104,6 +3104,35 @@ class TrainerIntegrationTest(TestCasePlus, TrainerIntegrationCommon):
                 trainer = Trainer(model=model, args=args, eval_dataset=eval_dataset)
             self.assertTrue("The `AcceleratorConfig`'s `num_steps` is set but" in str(context.exception))
 
+    def test_accelerator_config_not_instantiated(self):
+        # Checks that accelerator kwargs can be passed through
+        # and the accelerator is initialized respectively
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            with self.assertRaises(NotImplementedError) as context:
+                _ = RegressionTrainingArguments(
+                    output_dir=tmp_dir,
+                    accelerator_config=AcceleratorConfig,
+                )
+            self.assertTrue("Tried passing in a callable to `accelerator_config`" in str(context.exception))
+
+        # Now test with a custom subclass
+        @dataclasses.dataclass
+        class CustomAcceleratorConfig(AcceleratorConfig):
+            pass
+
+        @dataclasses.dataclass
+        class CustomTrainingArguments(TrainingArguments):
+            accelerator_config: dict = dataclasses.field(
+                default=CustomAcceleratorConfig,
+            )
+
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            with self.assertRaises(NotImplementedError) as context:
+                _ = CustomTrainingArguments(
+                    output_dir=tmp_dir,
+                )
+            self.assertTrue("Tried passing in a callable to `accelerator_config`" in str(context.exception))
+
 
 @require_torch
 @is_staging_test