Added Test for multi-index groupby partial indexing equivalence

pandas/tests/groupby/test_grouping.py

@@ -562,6 +562,37 @@ def test_groupby_multiindex_tuple(self):
         result = df.groupby(("b", 1)).groups
         tm.assert_dict_equal(expected, result)
 
+    def test_groupby_multiindex_partial_indexing_equivalence(self):
+        # GH 17977
+        df = DataFrame(
+            [[1, 2, 3, 4], [3, 4, 5, 6], [1, 4, 2, 3]],
+            columns=MultiIndex.from_arrays([["a", "b", "b", "c"], [1, 1, 2, 2]]),
+        )
+
+        expected_mean = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].mean()
+        result_mean = df.groupby([("a", 1)])["b"].mean()
+        tm.assert_frame_equal(expected_mean, result_mean)
+
+        expected_sum = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].sum()
+        result_sum = df.groupby([("a", 1)])["b"].sum()
+        tm.assert_frame_equal(expected_sum, result_sum)
+
+        expected_count = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].count()
+        result_count = df.groupby([("a", 1)])["b"].count()
+        tm.assert_frame_equal(expected_count, result_count)
+
+        expected_min = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].min()
+        result_min = df.groupby([("a", 1)])["b"].min()
+        tm.assert_frame_equal(expected_min, result_min)
+
+        expected_max = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].max()
+        result_max = df.groupby([("a", 1)])["b"].max()
+        tm.assert_frame_equal(expected_max, result_max)
+
+        expected_groups = df.groupby([("a", 1)])[[("b", 1), ("b", 2)]].groups
+        result_groups = df.groupby([("a", 1)])["b"].groups
+        tm.assert_dict_equal(expected_groups, result_groups)
+
     @pytest.mark.parametrize("sort", [True, False])
     def test_groupby_level(self, sort, mframe, df):
         # GH 17537