feat(test): test mypyc_attr(supports_weakref=True)

Author: BobTheBuidler

mypyc/test-data/irbuild-classes.test

@@ -1381,3 +1381,45 @@ class M(type):  # E: Inheriting from most builtin types is unimplemented
 @mypyc_attr(native_class=True)
 class A(metaclass=M):  # E: Class is marked as native_class=True but it can't be a native class. Classes with a metaclass other than ABCMeta, TypingMeta or GenericMeta can't be native classes.
     pass
+
+[case testMypycAttrSupportsWeakref]
+import weakref
+from mypy_extensions import mypyc_attr
+
+@mypyc_attr(supports_weakref=True)
+class WeakrefClass:
+    pass
+
+obj = WeakrefClass()
+ref = weakref.ref(obj)
+assert ref() is obj
+
+[case testMypycAttrSupportsWeakrefInheritance]
+import weakref
+from mypy_extensions import mypyc_attr
+
+@mypyc_attr(supports_weakref=True)
+class WeakrefClass:
+    pass
+
+class WeakrefInheritor(WeakrefClass):
+    pass
+
+obj = WeakrefInheritor()
+ref = weakref.ref(obj)
+assert ref() is obj
+
+[case testMypycAttrSupportsWeakrefSubclass]
+import weakref
+from mypy_extensions import mypyc_attr
+
+class NativeClass:
+    pass
+
+@mypyc_attr(supports_weakref=True)
+class WeakrefSubclass(NativeClass):
+    pass
+
+obj = WeakrefSubclass()
+ref = weakref.ref(obj)
+assert ref() is obj