Add more test cases

Author: Guido van Rossum

test-data/unit/check-classes.test

@@ -3157,3 +3157,37 @@ class M(type):
     x = 5
 class A(with_metaclass(M)): pass
 reveal_type(type(A).x)  # E: Revealed type is 'builtins.int'
+
+[case testSixWithMetaclassAndBase]
+import six
+class M(type):
+    x = 5
+class A:
+    def foo(self): pass
+class B:
+    def bar(self): pass
+class C1(six.with_metaclass(M, A)): pass
+class C2(six.with_metaclass(M, A, B)): pass
+reveal_type(type(C1).x)  # E: Revealed type is 'builtins.int'
+reveal_type(type(C2).x)  # E: Revealed type is 'builtins.int'
+C1().foo()
+C1().bar()  # E: "C1" has no attribute "bar"
+C2().foo()
+C2().bar()
+C2().baz()  # E: "C2" has no attribute "baz"
+
+[case testSixWithMetaclassErrors]
+import six
+class M(type): pass
+class A(object): pass
+class C1(six.with_metaclass(M), object): pass  # E: Invalid base class
+class C2(C1, six.with_metaclass(M)): pass  # E: Invalid base class
+class C3(six.with_metaclass(A)): pass  # E: Metaclasses not inheriting from 'type' are not supported
+class C4(six.with_metaclass(M), metaclass=M): pass  # E: Invalid base class
+
+[case testSixWithMetaclassErrors_python2-skip]
+# No error here yet
+import six
+class M(type): pass
+class C4(six.with_metaclass(M)):
+    __metaclass__ = M