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ELIXIR ADDS TRACE HELPER FOR ASYNC TEST ASSERTIONS
By RepoJournal · Filed · About Elixir & Phoenix · Composed from the cited sources · methodology
2 people shipped this
Elixir core shipped a new trace helper that solves the hardest problem in testing concurrent systems: asserting on state when you don't control the timing.
The trace helper lands in ExUnit.Assertions [1] and directly addresses a pattern that has frustrated Elixir developers testing LiveViews and GenServers subscribed to asynchronous messages. You trigger work in one process, another process delivers the result on its own schedule, and your test needs to assert on the final state without flaky sleeps or polling [2]. The helper lets you wait for specific trace events and assert on rendered output once they fire, turning a timing problem into a deterministic one. This started as a LiveView testing challenge [3] but the solution is generic enough to work anywhere you have inter-process communication. Phoenix LiveView also tightened upload validation, now raising when you try to render an upload entry that doesn't exist [4], catching bugs earlier in the development cycle instead of at runtime.
Action items
- → Update Elixir when new version ships and review trace helper docs for your async test patterns elixir-lang/elixir [plan]
- → Check LiveView tests using render_upload for non-existent entries and fix before upgrading phoenixframework/phoenix_live_view [plan]
References
- [1] Add trace helper to ExUnit.Assertions ↗ elixir-lang/elixir
- [2] Add trace helper to ExUnit.Assertions (#15432) ↗ elixir-lang/elixir
- [3] Validate render_upload entry ref ↗ phoenixframework/phoenix_live_view
- [4] Validate render_upload entry ref (#4272) ↗ phoenixframework/phoenix_live_view
