add test for indexing with single/double tuple

Author: ganevgv

pandas/tests/frame/indexing/test_indexing.py

@@ -2624,6 +2624,20 @@ 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])
+        df = pd.DataFrame([[tuple_1], [tuple_2]], columns=["A"]).set_index("A")
+
+        result = df.loc[[df.index[0]]]
+        expected = pd.DataFrame([[tuple_1]], columns=["A"]).set_index("A")
+        tm.assert_frame_equal(result, expected)
+
+        result = df.loc[[df.index[1]]]
+        expected = pd.DataFrame([[tuple_2]], columns=["A"]).set_index("A")
+        tm.assert_frame_equal(result, expected)
+
     def test_boolean_indexing(self):
         idx = list(range(3))
         cols = ["A", "B", "C"]