Fix test

Author: dcherian

xarray/core/groupby.py

@@ -787,14 +787,12 @@ def _maybe_restore_empty_groups(self, combined):
         """Our index contained empty groups (e.g., from a resampling or binning). If we
         reduced on that dimension, we want to restore the full index.
         """
-        from xarray.groupers import BinGrouper, TimeResampler
-
+        has_missing_groups = (
+            self.encoded.unique_coord.size != self.encoded.full_index.size
+        )
         indexers = {}
         for grouper in self.groupers:
-            if (
-                isinstance(grouper.grouper, BinGrouper | TimeResampler)
-                and grouper.name in combined.dims
-            ):
+            if has_missing_groups and grouper.name in combined._indexes:
                 indexers[grouper.name] = grouper.full_index
         if indexers:
             combined = combined.reindex(**indexers)

xarray/tests/test_groupby.py

@@ -2802,9 +2802,13 @@ def test_groupby_preserve_dtype(reduction):
     kwargs = {}
     if "nan" in reduction:
         kwargs["skipna"] = True
-        reduction = reduction.removeprefix("nan")
-    actual = getattr(ds.groupby("idx"), reduction)(**kwargs).test.dtype
+    # TODO: fix dtype with numbagg/bottleneck and use_flox=False
+    with xr.set_options(use_numbagg=False, use_bottleneck=False):
+        actual = getattr(ds.groupby("idx"), reduction.removeprefix("nan"))(
+            **kwargs
+        ).test.dtype
     expected = getattr(np, reduction)(ds.test.data, axis=0).dtype
+
     assert actual == expected