Fix h5netcdf backend module detection and ros3 tests (pydata#11274)

* use var._root._h5py to get h5py module in h5netcdf backend instead of importing it
* fix ros3 tests to use DANDI endpoint and include hdf5 version switch
* fix phony_dims for ros3 test
* fix import check for ros3 availability
* try using property to get around import issue
* add whats-new.rst entry

Author: kmuehlbauer

doc/whats-new.rst

@@ -121,6 +121,8 @@ Bug Fixes
   By `Emmanuel Ferdman <https://github.com/emmanuel-ferdman>`_.
 - :func:`combine_by_coords` no longer returns an empty dataset when a generator is passed as ``data_objects`` (:issue:`10114`, :pull:`11265`).
   By `Amartya Anand <https://github.com/SurfyPenguin>`_.
+- Fix h5netcdf backend module detection and ros3 tests (:issue:`11243`, :pull:`11274`).
+  By `Kai Mühlbauer <https://github.com/kmuehlbauer>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/backends/h5netcdf_.py

@@ -277,7 +277,6 @@ def ds(self):
 
     def open_store_variable(self, name, var):
         import h5netcdf.core
-        import h5py
 
         dimensions = var.dimensions
         data = indexing.LazilyIndexedArray(H5NetCDFArrayWrapper(name, self))
@@ -306,6 +305,7 @@ def open_store_variable(self, name, var):
         encoding["source"] = self._filename
         encoding["original_shape"] = data.shape
 
+        h5py = var._root._h5py
         vlen_dtype = h5py.check_dtype(vlen=var.dtype)
         if vlen_dtype is str:
             encoding["dtype"] = str

xarray/tests/__init__.py

@@ -215,9 +215,13 @@ def _importorskip_h5netcdf_ros3(has_h5netcdf: bool):
             not has_h5netcdf, reason="requires h5netcdf"
         )
 
-    import h5py
+    has_h5py, _ = _importorskip("h5py")
+    if has_h5py:
+        import h5py
 
-    h5py_with_ros3 = h5py.get_config().ros3
+        h5py_with_ros3 = h5py.get_config().ros3
+    else:
+        h5py_with_ros3 = has_h5py
 
     return h5py_with_ros3, pytest.mark.skipif(
         not h5py_with_ros3,

xarray/tests/test_backends.py

@@ -5422,29 +5422,46 @@ def test_memoryview_write_netcdf4_read_h5netcdf() -> None:
 @requires_h5netcdf_ros3
 class TestH5NetCDFDataRos3Driver(TestCommon):
     engine: T_NetcdfEngine = "h5netcdf"
-    test_remote_dataset: str = "https://archive.unidata.ucar.edu/software/netcdf/examples/OMI-Aura_L2-example.nc"
+    test_remote_dataset: str = "https://dandiarchive.s3.amazonaws.com/ros3test.hdf5"
+
+    @property
+    def ros3_kwargs(self) -> dict:
+        from h5py import version as h5ver
+
+        return (
+            {} if h5ver.hdf5_version_tuple < (2, 0, 0) else {"aws_region": b"us-east-2"}
+        )
 
     @pytest.mark.filterwarnings("ignore:Duplicate dimension names")
     def test_get_variable_list(self) -> None:
         with open_dataset(
             self.test_remote_dataset,
             engine="h5netcdf",
-            backend_kwargs={"driver": "ros3"},
+            backend_kwargs={
+                "driver": "ros3",
+                "driver_kwds": self.ros3_kwargs,
+                "phony_dims": "access",
+            },
         ) as actual:
-            assert "Temperature" in list(actual)
+            assert "mydataset" in list(actual)
 
     @pytest.mark.filterwarnings("ignore:Duplicate dimension names")
     def test_get_variable_list_empty_driver_kwds(self) -> None:
         driver_kwds = {
             "secret_id": b"",
             "secret_key": b"",
         }
-        backend_kwargs = {"driver": "ros3", "driver_kwds": driver_kwds}
+        driver_kwds.update(self.ros3_kwargs)
+        backend_kwargs = {
+            "driver": "ros3",
+            "driver_kwds": driver_kwds,
+            "phony_dims": "access",
+        }
 
         with open_dataset(
             self.test_remote_dataset, engine="h5netcdf", backend_kwargs=backend_kwargs
         ) as actual:
-            assert "Temperature" in list(actual)
+            assert "mydataset" in list(actual)
 
 
 @pytest.fixture(params=["scipy", "netcdf4", "h5netcdf", "zarr"])