D324 - Tests never choose shared resources by hand

Status: decided Date: 2026-09-26

A test reserving host memory takes its address from orbistoun-mem::test_bases, a table of per-crate ranges asserted distinct, which ships outside cfg(test). Process-wide state that is incidental to a test is passed in rather than reached for; where the shared state is what is under test, the tests that touch it are serialised behind an exclusive guard.

Why: tests run in parallel, within and across binaries, so two picking the same address race and fail intermittently. A per-binary counter cannot see other binaries, and a cfg(test) table is invisible to dependents, which would each define their own. A convention in prose was broken while it was being followed.

Rejected:

• Picking a gap by reading the file: the collision it prevents recurs.
• Per-crate test-only tables: two crates choose the same range.
• Passing state that is itself under test: there is nothing to pass.