moving join test to common.py

Author: erbian

pandas/tests/indexes/period/test_period.py

@@ -773,9 +773,3 @@ def test_map(self):
         result = index.map(lambda x: x.ordinal)
         exp = Index([x.ordinal for x in index])
         tm.assert_index_equal(result, exp)
-
-    @pytest.mark.parametrize('how', ['outer', 'inner', 'left', 'right'])
-    def test_join_self(self, how):
-        index = period_range('1/1/2000', periods=10)
-        joined = index.join(index, how=how)
-        assert index is joined