Provide pytest-plugin that registers a 'gpu' marker.

changes/+c563f4d4.bugfix.rst

@@ -0,0 +1 @@
+Register 'gpu' marker with pytest for downstream StoreTests.

pyproject.toml

@@ -455,3 +455,6 @@ issue_format = ":issue:`{issue}`"
 
 [tool.codespell]
 ignore-words-list = "astroid"
+
+[project.entry-points.pytest11]
+zarr = "zarr.testing"

src/zarr/testing/conftest.py

@@ -0,0 +1,9 @@
+import pytest
+
+
+def pytest_configure(config: pytest.Config) -> None:
+    # The tests in zarr.testing are intended to be run by downstream projects.
+    # To allow those downstream projects to run with `--strict-markers`, we need
+    # to register an entry point with pytest11 and register our "plugin" with it,
+    # which just registers the markers used in zarr.testing
+    config.addinivalue_line("markers", "gpu: mark a test as requiring CuPy and GPU")