1 files changed, 85 insertions, 0 deletions
diff --git a/pylint/test/functional/membership_protocol.py b/pylint/test/functional/membership_protocol.py
new file mode 100644
index 0000000..7b3a46f
--- /dev/null
+++ b/pylint/test/functional/membership_protocol.py
@@ -0,0 +1,85 @@
+# pylint: disable=missing-docstring,pointless-statement,expression-not-assigned,too-few-public-methods,import-error,no-init
+
+# standard types
+1 in [1, 2, 3]
+1 in {'a': 1, 'b': 2}
+1 in {1, 2, 3}
+1 in (1, 2, 3)
+1 in "123"
+1 in u"123"
+1 in bytearray(b"123")
+1 in frozenset([1, 2, 3])
+
+# comprehensions
+1 in [x ** 2 % 10 for x in range(10)]
+1 in {x ** 2 % 10 for x in range(10)}
+1 in {x: x ** 2 % 10 for x in range(10)}
+
+# iterators
+1 in iter([1, 2, 3])
+
+# generator
+def count(upto=float("inf")):
+    i = 0
+    while True:
+        if i > upto:
+            break
+        yield i
+        i += 1
+
+10 in count(upto=10)
+
+# custom instance
+class UniversalContainer(object):
+    def __contains__(self, key):
+        return True
+
+42 in UniversalContainer()
+
+# custom iterable
+class CustomIterable(object):
+    def __iter__(self):
+        return iter((1, 2, 3))
+3 in CustomIterable()
+
+# old-style iterable
+class OldStyleIterable(object):
+    def __getitem__(self, key):
+        if key < 10:
+            return 2 ** key
+        else:
+            raise IndexError("bad index")
+64 in OldStyleIterable()
+
+# do not emit warning if class has unknown bases
+from some_missing_module import ImportedClass
+
+class MaybeIterable(ImportedClass):
+    pass
+
+10 in MaybeIterable()
+
+# do not emit warning inside mixins
+class UsefulMixin(object):
+    stuff = None
+
+    def get_stuff(self):
+        return self.stuff
+
+    def act(self, thing):
+        stuff = self.get_stuff()
+        if thing in stuff:
+            pass
+
+# error cases
+42 in 42  # [unsupported-membership-test]
+42 not in None  # [unsupported-membership-test]
+42 in 8.5  # [unsupported-membership-test]
+
+class EmptyClass(object):
+    pass
+
+42 not in EmptyClass()  # [unsupported-membership-test]
+42 in EmptyClass  # [unsupported-membership-test]
+42 not in count  # [unsupported-membership-test]
+42 in range  # [unsupported-membership-test]