fix save_zarr code and test

Author: floriankrb

src/anemoi/datasets/data/misc.py

@@ -664,7 +664,7 @@ def initialize_zarr_store(root: Any, big_dataset: "Dataset") -> None:
     # Create or append to "dates" dataset.
     if "dates" not in root:
         full_length = len(big_dataset.dates)
-        root.create_dataset("dates", data=np.array([], dtype="datetime64[s]"), chunks=(full_length,))
+        root.create_dataset("dates", data=np.array([], dtype="datetime64[s]"), chunks=(full_length,), shape=(0,))
 
     if "data" not in root:
         dims = (1, len(big_dataset.variables), ensembles, big_dataset.shape[-1])
@@ -681,12 +681,15 @@ def initialize_zarr_store(root: Any, big_dataset: "Dataset") -> None:
                 k,
                 data=v,
                 compressor=None,
+                shape=v.shape,
             )
 
     # Create spatial coordinate datasets if missing.
     if "latitudes" not in root or "longitudes" not in root:
-        root.create_dataset("latitudes", data=big_dataset.latitudes, compressor=None)
-        root.create_dataset("longitudes", data=big_dataset.longitudes, compressor=None)
+        root.create_dataset("latitudes", data=big_dataset.latitudes, compressor=None, shape=big_dataset.latitudes.shape)
+        root.create_dataset(
+            "longitudes", data=big_dataset.longitudes, compressor=None, shape=big_dataset.longitudes.shape
+        )
     for k, v in big_dataset.metadata().items():
         if k not in root.attrs:
             root.attrs[k] = v

tests/test_data.py

@@ -42,6 +42,8 @@
 
 VALUES = 10
 
+true_zarr_open = zarr.open
+
 
 def mockup_open_zarr(func: Callable) -> Callable:
     """Decorator to mock the open_zarr function.
@@ -237,6 +239,8 @@ def zarr_from_str(name: str, mode: str) -> zarr.Group:
         Zarr dataset.
     """
     # Format: test-2021-2021-6h-o96-abcd-0
+    if "/" in name:
+        return true_zarr_open(name)
 
     args = dict(
         test="test",