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Elixir & Phoenix

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The Wire · Showcase

ELIXIR ADDS TRACE HELPER FOR ASYNC TEST ASSERTIONS

By RepoJournal · Filed · About Elixir & Phoenix

Stop guessing when your GenServer will receive that PubSub message. Elixir's new trace helper lets you assert on async process state without the timing games.

Elixir shipped a trace helper for ExUnit.Assertions [1] that solves a real pain point in testing: waiting for messages to arrive at processes you don't directly control. The problem started in LiveView testing [2] where you'd trigger work in one process and need to assert on state changes in another, but the timing was never guaranteed. Now you can write assertions that wait for the right trace event instead of adding flaky sleeps or complex polling loops.

Phoenix LiveView tightened validation around render_upload [3] by raising when you try to render an entry that doesn't exist. This catches bugs earlier instead of silently returning undefined behavior. It's a small safety improvement, but one that ships with 4.0 and will affect anyone relying on implicit nil handling for missing uploads.

Action items

References

  1. [1] Add trace helper to ExUnit.Assertions ↗ elixir-lang/elixir
  2. [2] Validate render_upload entry ref ↗ phoenixframework/phoenix_live_view
  3. [3] Validate render_upload entry ref (#4272) phoenixframework/phoenix_live_view

FAQ

What changed in Elixir & Phoenix on June 8, 2026?
Stop guessing when your GenServer will receive that PubSub message. Elixir's new trace helper lets you assert on async process state without the timing games.
What should Elixir & Phoenix teams do about it?
Review your async LiveView and GenServer tests for trace opportunities • Check render_upload calls for missing entry refs before upgrading to Phoenix LiveView 4.0
Which Elixir & Phoenix repositories shipped on June 8, 2026?
elixir-lang/elixir, phoenixframework/phoenix_live_view

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