Make sure to pass through range indexes (#225)

Author: dcherian

flox/core.py

@@ -1508,7 +1508,7 @@ def _convert_expected_groups_to_index(
 ) -> tuple[pd.Index | None, ...]:
     out: list[pd.Index | None] = []
     for ex, isbin_ in zip(expected_groups, isbin):
-        if isinstance(ex, pd.IntervalIndex) or (isinstance(ex, pd.Index) and not isbin):
+        if isinstance(ex, pd.IntervalIndex) or (isinstance(ex, pd.Index) and not isbin_):
             if sort:
                 ex = ex.sort_values()
             out.append(ex)

tests/test_core.py

@@ -1316,3 +1316,12 @@ def test_negative_index_factorize_race_condition():
         for f in func
     ]
     [dask.compute(out, scheduler="threads") for _ in range(5)]
+
+
+@pytest.mark.parametrize("sort", [True, False])
+def test_expected_index_conversion_passthrough_range_index(sort):
+    index = pd.RangeIndex(100)
+    actual = _convert_expected_groups_to_index(
+        expected_groups=(index,), isbin=(False,), sort=(sort,)
+    )
+    assert actual[0] is index