TST: add test for indexing with single/double tuples

pandas/tests/frame/test_indexing.py

@@ -2626,6 +2626,23 @@ def test_index_namedtuple(self):
         result = df.loc[IndexType("foo", "bar")]["A"]
         assert result == 1
 
+    def test_index_single_double_tuples(self):
+        # GH 20991
+        tuple_1 = tuple([1, 2])
+        tuple_2 = tuple([1])
+        idx = pd.Index([tuple_1, tuple_2], name="A", tupleize_cols=False)
+        df = DataFrame(index=idx)
+
+        result = df.loc[[tuple_1]]
+        idx_1 = pd.Index([tuple_1], name="A", tupleize_cols=False)
+        expected = DataFrame(index=idx_1)
+        tm.assert_frame_equal(result, expected)
+
+        result = df.loc[[tuple_2]]
+        idx_2 = pd.Index([tuple_2], name="A", tupleize_cols=False)
+        expected = DataFrame(index=idx_2)
+        tm.assert_frame_equal(result, expected)
+
     def test_boolean_indexing(self):
         idx = list(range(3))
         cols = ["A", "B", "C"]