add regression test

Author: benbovy

xarray/testing/assertions.py

@@ -273,7 +273,7 @@ def _assert_indexes_invariants_checks(
         if isinstance(index, PandasIndex):
             pd_index = index.index
             var = possible_coord_variables[k]
-            assert (index.dim,) == var.dims, (pd_index, var)
+            assert (index.dim,) == var.dims, (index, index.dim, var)
             if k == index.dim:
                 # skip multi-index levels here (checked below)
                 assert index.coord_dtype == var.dtype, (index.coord_dtype, var.dtype)

xarray/tests/test_dataset.py

@@ -3251,6 +3251,13 @@ def test_swap_dims(self) -> None:
         assert isinstance(actual.variables["x"], Variable)
         assert actual.xindexes["y"].equals(expected.xindexes["y"])
 
+    def test_swap_dims_after_rename_vars(self) -> None:
+        # https://github.com/pydata/xarray/issues/8646
+        ds = Dataset(coords={"y": [1, 2]})
+        actual = ds.rename_vars(y="z").swap_dims(y="z")
+        expected = Dataset(coords={"z": [1, 2]})
+        assert_identical(actual, expected)
+
     def test_expand_dims_error(self) -> None:
         original = Dataset(
             {