Update mock behaviour (#10207)

* 解决了`DummyModule`在`isinstance`因为是实例而会报错的问题
* 为其增加`__enter__`和`__exit__`的报错
* 完成以上的unittest

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

python/oneflow/mock_torch/__init__.py

@@ -248,6 +248,22 @@ def __bool__(self):
             )
         return False
 
+    def __enter__(self):
+        raise RuntimeError(
+            f'"{self.__name__}" is a dummy object, and does not support "with" statement.'
+        )
+
+    def __exit__(self, exception_type, exception_value, traceback):
+        raise RuntimeError(
+            f'"{self.__name__}" is a dummy object, and does not support "with" statement.'
+        )
+
+    def __subclasscheck__(self, subclass):
+        return False
+
+    def __instancecheck__(self, instance):
+        return False
+
 
 class enable:
     def __init__(

python/oneflow/test/misc/test_mock_scope.py

@@ -180,6 +180,24 @@ def test_hazard_list(test_case):
         test_case.assertTrue("safetensors._safetensors_rust" in sys.modules)
         import safetensors
 
+    def test_isinstance(test_case):
+        with mock.enable(lazy=True):
+            import torch
+
+            test_case.assertFalse(isinstance(int, torch._six.string_class))
+
+    def test_with_statement(test_case):
+        with mock.enable(lazy=True):
+            with test_case.assertRaises(RuntimeError) as context:
+                import torch.noexist
+
+                with torch.noexist:
+                    pass
+            test_case.assertTrue(
+                '"oneflow.noexist" is a dummy object, and does not support "with" statement.'
+                in str(context.exception)
+            )
+
 
 # MUST use pytest to run this test
 def test_verbose(capsys):