Fix check for chunk_store in zarr backend (#7923)

* Fix check for chunk_store in zarr backend

* Add test and update whats-new

* Update the whats-new message

Author: juntyr

doc/whats-new.rst

@@ -61,6 +61,8 @@ Bug fixes
   By `Tom White <https://github.com/tomwhite>`_ and `Kai Mühlbauer <https://github.com/kmuehlbauer>`_.
 - Ensure dtype of reindex result matches dtype of the original DataArray (:issue:`7299`, :pull:`7917`)
   By `Anderson Banihirwe <https://github.com/andersy005>`_.
+- Fix bug where a zero-length zarr ``chunk_store`` was ignored as if it was ``None`` (:pull:`7923`)
+  By `Juniper Tyree <https://github.com/juntyr>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/backends/zarr.py

@@ -417,7 +417,7 @@ def open_group(
             if consolidated is None:
                 consolidated = False
 
-        if chunk_store:
+        if chunk_store is not None:
             open_kwargs["chunk_store"] = chunk_store
             if consolidated is None:
                 consolidated = False

xarray/tests/test_backends.py

@@ -1849,6 +1849,8 @@ def test_with_chunkstore(self) -> None:
         with self.create_zarr_target() as store_target, self.create_zarr_target() as chunk_store:
             save_kwargs = {"chunk_store": chunk_store}
             self.save(expected, store_target, **save_kwargs)
+            # the chunk store must have been populated with some entries
+            assert len(chunk_store) > 0
             open_kwargs = {"backend_kwargs": {"chunk_store": chunk_store}}
             with self.open(store_target, **open_kwargs) as ds:
                 assert_equal(ds, expected)