Validate cached snapshot tests against expected metadata#2679
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A cached snapshot test result could be reused after the expected snapshot changed on disk, as long as the test code content hash still matched. This showed up when switching git branches: snapshots/output still reflected the old run, snapshots/expected could have been updated, and acton test would trust the cached pass. This change makes cached snapshot reuse check the on-disk snapshot artifacts before accepting the cached result. We only reuse the cache when snapshots/output/<module>/<test> exists, the expected snapshot exists, the file sizes match, and the expected snapshot mtime is older than the output snapshot mtime. Any uncertainty falls back to rerunning the test, which keeps cache hits cheap while conservatively avoiding stale snapshot passes. A regression test was added for acton test to cover the branch-switch style scenario where the expected snapshot changes without any source change, and the testing docs were updated to describe the extra snapshot validation.
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A cached snapshot test result could be reused after the expected snapshot changed on disk, as long as the test code content hash still matched. This showed up when switching git branches: snapshots/output still reflected the old run, snapshots/expected could have been updated, and acton test would trust the cached pass.
This change makes cached snapshot reuse check the on-disk snapshot artifacts before accepting the cached result. We only reuse the cache when snapshots/output// exists, the expected snapshot exists, the file sizes match, and the expected snapshot mtime is older than the output snapshot mtime. Any uncertainty falls back to rerunning the test, which keeps cache hits cheap while conservatively avoiding stale snapshot passes.
A regression test was added for acton test to cover the branch-switch style scenario where the expected snapshot changes without any source change, and the testing docs were updated to describe the extra snapshot validation.