Add tests

Author: srittau

stdlib/@tests/test_cases/check_operator.py

@@ -0,0 +1,11 @@
+from operator import methodcaller
+from typing import Any
+from typing_extensions import assert_type
+
+m1 = methodcaller("foo")
+assert_type(m1, methodcaller[[], Any])
+m2 = methodcaller("foo", 42, bar="")
+# assert_type(m2, methodcaller[[int, Arg(str, "bar")], Any])
+m3: methodcaller[[], int] = methodcaller("foo")  # ok
+m4: methodcaller[[int], Any] = methodcaller("foo", 1)  # ok
+m5: methodcaller[[str], int] = methodcaller("foo", 1)  # type: ignore