Test open_mfdataset_manyfiles with engine zarr

Zarr objects are folders with seem to cause issues with closing, so added a try-except to api.py to catch failures in f.close(). Some tests failing when chunks=None because a numpy array is returned instead of a dask array.

xarray/backends/api.py

@@ -774,7 +774,10 @@ def __init__(self, file_objs):
 
     def close(self):
         for f in self.file_objs:
-            f.close()
+            try:
+                f.close()
+            except AttributeError:  # 'NoneType' object has no attribute 'close'
+                pass
 
 
 def open_mfdataset(

xarray/tests/test_backends.py

@@ -2507,7 +2507,7 @@ def test_write_inconsistent_chunks(self):
             assert actual["y"].encoding["chunksizes"] == (100, 50)
 
 
-@pytest.fixture(params=["scipy", "netcdf4", "h5netcdf", "pynio"])
+@pytest.fixture(params=["scipy", "netcdf4", "h5netcdf", "pynio", "zarr"])
 def readengine(request):
     return request.param
 
@@ -2567,7 +2567,10 @@ def test_open_mfdataset_manyfiles(
         # split into multiple sets of temp files
         for ii in original.x.values:
             subds = original.isel(x=slice(ii, ii + 1))
-            subds.to_netcdf(tmpfiles[ii], engine=writeengine)
+            if writeengine != "zarr":
+                subds.to_netcdf(tmpfiles[ii], engine=writeengine)
+            else:  # if writeengine == "zarr":
+                subds.to_zarr(store=tmpfiles[ii])
 
         # check that calculation on opened datasets works properly
         with open_mfdataset(