# `Tack.Credo.Check.SleepInTest`
[🔗](https://github.com/giggleton/pica/blob/v0.1.0/dev/tack/credo/check/sleep_in_test.ex#L1)

## Basics

> #### This check is disabled by default. {: .neutral}
>
> [Learn how to enable it](`e:credo:config_file.html#checks`) via `.credo.exs`.

This check has a base priority of `high` and works with any version of Elixir.

## Explanation

A test that waits for something asynchronous polls the condition with the suite's
`eventually/2` helper (`test/support/eventually.ex`), never a sleep.

`elixir-code-review`, `references/test-quality.md`:

> **Wait with `eventually/2`, never a hand-rolled loop.** A test that waits for an
> asynchronous condition calls `eventually/2` (or `eventually_render/3` against a LiveView):
> one documented budget, and it always flunks when time runs out.

A bare `Process.sleep(n)` in a test is one of two things, and both are findings:

  * **a guess** — "the cast has surely landed by now". It is flaky under load and slow when
    idle, and the fix is to wait on the condition itself with `eventually/2`.
  * **a polling loop** — the sleep inside a hand-written retry. Every such loop picks its
    own budget, and some return `false` or `:ok` on timeout and rely on every caller to
    `assert`, so a test whose condition never came true can pass. Each new test copies
    whichever loop sits nearest.

Scope the check to `test/` and exclude `test/support/` in `.credo.exs`: that is where the one
sanctioned loop lives. `Process.sleep(:infinity)` is out of scope too — it parks a process
(a holder that must stay alive until the test kills it) and guesses at no timing.

What remains is a sleep that *is* the subject: an absence held for a window ("the supervisor
must not restart it"), a TTL that must lapse on the wall clock, a gap staged between two
events with no signal to wait on. Those carry an inline waiver that says so.

## Check-Specific Parameters

*There are no specific parameters for this check.*

## General Parameters

Like with all checks, [general params](`e:credo:check_params.html`) can be applied.

Parameters can be configured via the [`.credo.exs` config file](`e:credo:config_file.html`).

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*Consult [api-reference.md](api-reference.md) for complete listing*