Tests should be deterministic, isolated, and assert the intended behavior (not just a coincidence or shared prior state). Concretely: - Reset external/shared state for every test (especially Redis, quotas, counters). Do not rely on the order tests run. - Avoid vacuous assertions and shared artifacts (e.g., “last line in a shared file”) that can match data from earlier blocks. - When testing stateful backends, prefer multi-worker coverage so race/state behavior is exercised. - Keep test scaffolding minimal—remove dead/irrelevant setup that doesn’t actually reach the code under test. - Use fixed test inputs/identifiers where applicable to avoid flakiness. Example (state reset + independent setup): ```perl add_block_preprocessor(sub { my ($block) = @_; # Ensure Redis-backed tests start from a known state require("lib.test_redis").flush_all(); # Optionally set a deterministic default request if (!$block->request) { $block->set_value("request", "GET /t"); } }); ``` Example (avoid shared-state/vacuous “tail -n 1”): - Don’t assert against a shared “last export” file unless you can correlate the export to the current request. - If you must pattern-match, make the pattern reject the forbidden value (e.g., all-zero) instead of only matching a broad UUID/hex shape. Apply this standard when adding or modifying tests in the Testing category to reduce CI flakiness and increase confidence in coverage.