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Example scripts now run once, in a new Example scripts CI job, instead of in every pytest matrix job. tests/test_examples.py uses uv add --script to point each script's PEP 723 header at the local checkout, and runs the script with uv run.

Why

• Each example runs in an environment built from its own header, so every matrix job ran the same thing.
• The old test rewrote headers with a regex, tomlkit and packaging, which run in the test environment. In zarr-python PR 4544 this broke the min_deps job: with packaging==22.* on Python 3.12.3, the URL zarr @ file:////home/... (four slashes) is rejected as invalid.
• uv add resolves the header. That showed that sharding_coalescing.py and codec_pipeline_performance.py declared requires-python = ">=3.11", although zarr requires 3.12. Both headers now say >=3.12.

Changes

• tests/test_examples.py: one test per example, marked examples. The test copies the script, runs uv add --script <copy> <checkout>, then runs uv run --reinstall-package zarr <copy>. The regex, tomlkit and packaging code is gone. The checkout path now comes from __file__ instead of the working directory. The Windows skip is removed, because no Windows job runs these tests.
• tests/conftest.py: new --run-examples option. Tests marked examples are skipped without it, in the same way that slow_hypothesis tests are skipped without --run-slow-hypothesis. The matrix jobs therefore skip them without any change to their commands.
• pyproject.toml: registers the examples marker, and removes tomlkit from the test dependency group, which had no other users. uv stays, because tests/test_regression/test_v2_dtype_regression.py uses it.
• Justfile: new test-examples recipe, which runs pytest --run-examples tests/test_examples.py.
• .github/workflows/test.yml: new examples job, which runs just test-examples in the test.py3.13-minimal hatch environment. It is added to test-complete.
• examples/README.md: says that an example needs a PEP 723 header, and how examples are run.

Testing

• HATCH_ENV=test.py3.13-minimal just test-examples passes locally: the path check and all three examples.
• Without --run-examples, the three example tests are skipped. slow_hypothesis tests are still skipped without --run-slow-hypothesis.
• With two examples broken at once (one exits non-zero, one has a >=3.11 header), both tests fail with their own message, and the third example still runs.
• prek run --all-files passes.

Notes

• The first commit ran the examples from a bash loop in the Justfile. The second commit replaces it with pytest, because the loop stopped at the first failing example and hid the others.
• No changelog fragment: the change affects CI and contributors, not library users.
• ci/big-endian/Dockerfile still installs python3-tomlkit. The big-endian job does not run this test, so the package is unused there. The agent left the image unchanged because it could not build the s390x image locally.

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[d-v-b]

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Superseded by zarr-developers#4586, which merged this branch upstream.