start writing tests

conftest.py

@@ -48,6 +48,19 @@ def netcdf4_file(tmpdir):
     return filepath
 
 
+@pytest.fixture
+def chunked_netcdf4_file(tmpdir):
+    # Set up example xarray dataset
+    ds = xr.tutorial.open_dataset("air_temperature")
+
+    # Save it to disk as netCDF (in temporary directory)
+    filepath = f"{tmpdir}/air.nc"
+    ds.chunk(time=1460).to_netcdf(filepath, format="NETCDF4")
+    ds.close()
+
+    return filepath
+
+
 @pytest.fixture
 def netcdf4_file_with_data_in_multiple_groups(tmpdir):
     filepath = str(tmpdir / "test.nc")

virtualizarr/backend.py

@@ -255,7 +255,7 @@ def open_virtual_mfdataset(
     combine_attrs: "CombineAttrsOptions" = "override",
     **kwargs,
 ) -> Dataset:
-    """Open multiple files as a single virtual dataset
+    """Open multiple files as a single virtual dataset.
 
     If combine='by_coords' then the function ``combine_by_coords`` is used to combine
     the datasets into one before returning the result, and if combine='nested' then
@@ -307,7 +307,7 @@ def open_virtual_mfdataset(
 
     # TODO this is practically all just copied from xarray.open_mfdataset - an argument for writing a virtualizarr engine for xarray?
 
-    # TODO add options passed to open_virtual_dataset explicitly?
+    # TODO list kwargs passed to open_virtual_dataset explicitly?
 
     paths = _find_absolute_paths(paths)
 

virtualizarr/tests/test_backend.py

@@ -8,7 +8,7 @@
 from xarray import Dataset, open_dataset
 from xarray.core.indexes import Index
 
-from virtualizarr import open_virtual_dataset
+from virtualizarr import open_virtual_dataset, open_virtual_mfdataset
 from virtualizarr.backend import FileType, automatically_determine_filetype
 from virtualizarr.manifests import ManifestArray
 from virtualizarr.readers import HDF5VirtualBackend
@@ -440,6 +440,41 @@ def test_open_dataset_with_scalar(self, hdf5_scalar, tmpdir, hdf_backend):
         assert vds.scalar.attrs == {"scalar": "true"}
 
 
+class TestOpenVirtualMFDataset:
+    def test_serial(self, netcdf4_files_factory, chunked_netcdf4_file):
+        filepath1, filepath2 = netcdf4_files_factory()
+
+        combined_vds = open_virtual_mfdataset(
+            [filepath1, filepath2],
+            combine="nested",
+            concat_dim="time",
+            coords="minimal",
+            compat="override",
+            indexes={},
+        )
+        expected_vds = open_virtual_dataset(chunked_netcdf4_file, indexes={})
+        print(combined_vds["air"].data)
+        print(expected_vds["air"].data)
+        xrt.assert_identical(combined_vds, expected_vds)
+
+        combined_vds = open_virtual_mfdataset(
+            [filepath1, filepath2], combine="by_coords"
+        )
+        expected_vds = open_virtual_dataset(chunked_netcdf4_file)
+        xrt.assert_identical(combined_vds, expected_vds)
+
+        file_glob = filepath1.parent.with_suffix("air*.nc")
+        combined_vds = open_virtual_mfdataset(file_glob, combine="by_coords")
+        expected_vds = open_virtual_dataset(chunked_netcdf4_file)
+        xrt.assert_identical(combined_vds, expected_vds)
+
+    # @requires_dask
+    def test_dask(self, netcdf4_files_factory): ...
+
+    # @requires_lithops
+    def test_lithops(self, netcdf4_files_factory): ...
+
+
 @requires_kerchunk
 @pytest.mark.parametrize(
     "reference_format",