chore: speed up test suite with pytest-xdist parallelization

pyproject.toml

@@ -141,6 +141,8 @@ exclude_also = [
 ]
 
 [tool.coverage.run]
+parallel = true
+source = ["src"]
 omit = [
     "bench/compress_normal.py",
     "src/zarr/testing/conftest.py",  # only for downstream projects
@@ -156,6 +158,7 @@ hooks.vcs.version-file = "src/zarr/_version.py"
 dependency-groups = ["test"]
 
 [tool.hatch.envs.test.env-vars]
+COVERAGE_PROCESS_START = "pyproject.toml"
 
 [[tool.hatch.envs.test.matrix]]
 python = ["3.12", "3.13", "3.14"]
@@ -173,18 +176,21 @@ matrix.deps.dependency-groups = [
 
 [tool.hatch.envs.test.scripts]
 run-coverage = [
-    "coverage run --source=src -m pytest --ignore tests/benchmarks --junitxml=junit.xml -o junit_family=legacy {args:}",
+    "coverage run -m pytest -n auto --dist loadgroup --ignore tests/benchmarks --junitxml=junit.xml -o junit_family=legacy {args:}",
+    "coverage combine",
     "coverage xml",
 ]
 run-coverage-html = [
-    "coverage run --source=src -m pytest --ignore tests/benchmarks {args:}",
+    "coverage run -m pytest -n auto --dist loadgroup --ignore tests/benchmarks {args:}",
+    "coverage combine",
     "coverage html",
 ]
-run = "pytest --ignore tests/benchmarks"
+run = "pytest -n auto --dist loadgroup --ignore tests/benchmarks {args:}"
 run-verbose = "run-coverage --verbose"
 run-mypy = "mypy src"
 run-hypothesis = [
-    "coverage run --source=src -m pytest -nauto --run-slow-hypothesis tests/test_properties.py tests/test_store/test_stateful* {args:}",
+    "coverage run -m pytest -nauto --dist loadgroup --run-slow-hypothesis tests/test_properties.py tests/test_store/test_stateful* {args:}",
+    "coverage combine",
     "coverage xml",
 ]
 run-benchmark = "pytest --benchmark-enable tests/benchmarks"
@@ -203,7 +209,8 @@ python = ["3.12", "3.13"]
 
 [tool.hatch.envs.gputest.scripts]
 run-coverage = [
-    "coverage run --source=src -m pytest -m gpu --junitxml=junit.xml -o junit_family=legacy --ignore tests/benchmarks {args:}",
+    "coverage run -m pytest -m gpu --junitxml=junit.xml -o junit_family=legacy --ignore tests/benchmarks {args:}",
+    "coverage combine",
     "coverage xml",
 ]
 run = "pytest -m gpu --ignore tests/benchmarks"

tests/test_api/test_synchronous.py

@@ -93,7 +93,7 @@ def test_docstrings_match(callable_name: str) -> None:
             ),
         ),
     ],
-    ids=str,
+    ids=["store_path-create_array_group", "store_path-create", "array_params-create_array_dataset"],
 )
 def test_docstring_consistent_parameters(
     parameter_name: str, array_creation_routines: tuple[Callable[[Any], Any], ...]

tests/test_store/test_fsspec.py

@@ -44,6 +44,9 @@
     pytest.mark.filterwarnings(
         "ignore:Exception ignored in.*finalize object.*:pytest.PytestUnraisableExceptionWarning"
     ),
+    # All S3 tests share a module-scoped moto server on a fixed port,
+    # so they must run on a single xdist worker to avoid port conflicts.
+    pytest.mark.xdist_group(name="s3"),
 ]
 
 fsspec = pytest.importorskip("fsspec")