TST: MultiIndex Slicing maintains first level index (#12697) (#15255)

Author: mroeschke

pandas/tests/indexing/test_indexing.py

@@ -5392,6 +5392,23 @@ def test_maybe_numeric_slice(self):
  expected = [1]
  self.assertEqual(result, expected)
 
+ def test_multiindex_slice_first_level(self):
+ # GH 12697
+ freq = ['a', 'b', 'c', 'd']
+ idx = pd.MultiIndex.from_product([freq, np.arange(500)])
+ df = pd.DataFrame(list(range(2000)), index=idx, columns=['Test'])
+ df_slice = df.loc[pd.IndexSlice[:, 30:70], :]
+ result = df_slice.loc['a']
+ expected = pd.DataFrame(list(range(30, 71)),
+ columns=['Test'],
+ index=range(30, 71))
+ tm.assert_frame_equal(result, expected)
+ result = df_slice.loc['d']
+ expected = pd.DataFrame(list(range(1530, 1571)),
+ columns=['Test'],
+ index=range(30, 71))
+ tm.assert_frame_equal(result, expected)
+
 
 class TestSeriesNoneCoercion(tm.TestCase):
  EXPECTED_RESULTS = [