Add tests.

xarray/core/parallel.py

@@ -350,7 +350,7 @@ def _wrapper(func, args, kwargs, arg_is_array, expected_shapes):
         if isinstance(template, DataArray):
             output_chunks = dict(zip(template.dims, template.chunks))  # type: ignore
         else:
-            output_chunks = template.chunks
+            output_chunks = dict(template.chunks)
 
     if isinstance(template, DataArray):
         result_is_array = True

xarray/tests/test_dask.py

@@ -1092,6 +1092,36 @@ def test_map_blocks_convert_args_to_list(obj):
     assert_identical(actual, expected)
 
 
+def test_map_blocks_dask_args():
+    da1 = xr.DataArray(
+        np.ones((10, 20)),
+        dims=["x", "y"],
+        coords={"x": np.arange(10), "y": np.arange(20)},
+    ).chunk({"x": 5, "y": 4})
+
+    # check that block shapes are the same
+    def sumda(da1, da2):
+        assert da1.shape == da2.shape
+        return da1 + da2
+
+    da2 = da1 + 1
+    with raise_if_dask_computes():
+        mapped = xr.map_blocks(sumda, da1, args=[da2])
+    xr.testing.assert_equal(da1 + da2, mapped)
+
+    # one dimension in common
+    da2 = (da1 + 1).isel(x=1, drop=True)
+    with raise_if_dask_computes():
+        mapped = xr.map_blocks(operator.add, da1, args=[da2])
+    xr.testing.assert_equal(da1 + da2, mapped)
+
+    # test that everything works when dimension names are different
+    da2 = (da1 + 1).isel(x=1, drop=True).rename({"y": "k"})
+    with raise_if_dask_computes():
+        mapped = xr.map_blocks(operator.add, da1, args=[da2])
+    xr.testing.assert_equal(da1 + da2, mapped)
+
+
 @pytest.mark.parametrize("obj", [make_da(), make_ds()])
 def test_map_blocks_add_attrs(obj):
     def add_attrs(obj):