Skip to content

ADR 085: A test fixture is named at random, not from the clock

This page is generated from docs/decisions/*.yaml by task docs:export-adr-markdown. Do not edit manually.

  • Number: 085
  • Title: A test fixture is named at random, not from the clock
  • Category: development
  • Status: accepted
  • Provenance: guided-ai
  • Source: docs/decisions/085-a-test-fixture-is-named-at-random.yaml

Decision

A test that creates a fixture on a server names it with testsupport.UniqueSuffix or testsupport.UniqueName, which draw from crypto/rand. Not a timestamp, not a timestamp with a counter beside it, and not a timestamp cut down to fit. The prefix stays readable, so a fixture left behind can be traced to the test that made it; only the unique part is random. This refines ADR-015's unique per-test namespaces.

Agent Instructions

Use testsupport.UniqueSuffix or testsupport.UniqueName for anything a test creates that the server requires to be unique. Upper-case a value Bitbucket stores upper-cased, such as a project key. TestNoFixtureIsNamedFromTheClock fails a string built from time.Now() through fmt.Sprint*, strconv or concatenation, directly or through a local variable. A clock value that is not a name, such as a query window, carries a clock-value-not-a-name comment giving the reason.

Rationale

Clock-derived names collided in three ways, each first misread as a product bug. Truncated, they repeat within a run. The clock is coarser than the suite is parallel, so two tests read the same value. And a counter beside the clock restarts with the process, so a run collides with the fixtures a crashed run left behind. Randomness removes all three, and the reasoning about them.

Rejected Alternatives

  • Widen the timestamps until collisions stop: Each widening answers one cause and leaves the others: a full-resolution timestamp still repeats when the clock is coarse, and across runs when a counter is what makes it unique.
  • Clean the instance before every run: It depends on a teardown that a crash is exactly what prevents, and does nothing about two tests colliding inside one run.