test: fs: stop the disk space test racing with the filesystem - #442
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`a_requirement_beyond_the_available_space_is_rejected` read the free space, then handed the very same number to `ensure_disk_space`, which reads it again. Any other writer on that filesystem moves the second reading, and the boundary case the test was pinned to then falls on the wrong side. It failed exactly that way in the coverage step of https://github.com/UpdateHub/updatehub/actions/runs/32294740390, with `available: 80615378944, required: 80615387136`: 8 KiB vanished while the two readings ran, because `cargo llvm-cov` has the parallel tests writing .profraw files the whole time. Step back from the boundary on both sides. Half of the free space stays available however busy the disk gets, and no filesystem answers with `u64::MAX`, so the rejection no longer depends on what the second reading finds.
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a_requirement_beyond_the_available_space_is_rejectedread the free space, then handed the very same number toensure_disk_space, which reads it again:Any other writer on that filesystem moves the second reading, so the boundary case the test was pinned to falls on the wrong side.
It failed exactly that way in the coverage step of run 32294740390:
8 KiB vanished while the two readings ran, because
cargo llvm-covhas the parallel tests writing.profrawfiles the whole time.The fix
Step back from the boundary on both sides. Half of the free space stays available however busy the disk gets, and no filesystem answers with
u64::MAX, so the rejection no longer depends on what the second reading finds.This blocks #441, which the same flake failed on with an unrelated diff.
Verification
cargo test --lib utils::fs: 11 pass, 0 fail.cargo fmt --all -- --check: clean.cargo clippy --locked --all-features --all --tests -- -D clippy::all: clean.