xfail for cross engine read write netcdf4

xarray/tests/test_backends.py

@@ -1025,13 +1025,11 @@ def test_complex(self):
         with self.roundtrip(expected) as actual:
             self.assertDatasetEqual(expected, actual)
 
+    @pytest.mark.xfail(reason='https://github.com/pydata/xarray/issues/535')
     def test_cross_engine_read_write_netcdf4(self):
         # Drop dim3, because its labels include strings. These appear to be
         # not properly read with python-netCDF4, which converts them into
         # unicode instead of leaving them as bytes.
-        if PY3:
-            raise unittest.SkipTest('see https://github.com/pydata/xarray/issues/535')
-
         data = create_test_data().drop('dim3')
         data.attrs['foo'] = 'bar'
         valid_engines = ['netcdf4', 'h5netcdf']