Run array API tests on Zarr Python 2 and 3 (#733)

Author: tomwhite

.github/workflows/array-api-tests.yml

@@ -22,6 +22,7 @@ jobs:
       matrix:
         os: ["ubuntu-latest"]
         python-version: ["3.11"]
+        zarr: ["<3", ">3"]
 
     steps:
       - name: Checkout Cubed
@@ -44,8 +45,10 @@ jobs:
         run: |
           pushd array-api-tests
           pip install -e '../cubed[test]'
-          pip install -U 'zarr<3'
           pip install -r requirements.txt  # from Array API tests repo
+      - name: Install zarr${{ matrix.zarr }}
+        run: |
+          pip install -U 'zarr${{ matrix.zarr }}'
       - name: Run Array API tests
         env:
           ARRAY_API_TESTS_MODULE: cubed.array_api

cubed/storage/backends/zarr_python_v3.py

@@ -4,6 +4,9 @@
 
 from cubed.types import T_DType, T_RegularChunks, T_Shape, T_Store
 
+# always write empty chunks to avoid a check for each chunk
+zarr.config.set({"array.write_empty_chunks": True})
+
 
 class ZarrV3ArrayGroup(dict):
     def __init__(