Test Registered After Collection

ID

javascript.async_test_registration

Severity

critical

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Reliability

Language

JavaScript

Tags

async, reliability, testing

Description

Reports an it(…​) or test(…​) declared from inside an async callback or a .then() continuation.

Every JavaScript runner collects a file’s tests synchronously: it runs the module and the suite callbacks once, records the declarations it saw, then starts executing them. A declaration that happens after the first await, or in a continuation that resolves on a later turn of the event loop, happens after collection has closed.

The whole chain of enclosing functions is examined, so a test nested several callbacks deep inside an async suite is reported too. The test’s own callback may of course be async — that is the ordinary way to write an asynchronous test and is never reported.

Rationale

// Bad
describe('rates', async () => {
  const rates = await loadRates();

  it('converts euros', () => {          // collected too late, never runs
    expect(convert(rates, 10)).toBe(12);
  });
});

  • The suite is quietly smaller than the file: the runner reports the tests it collected and says nothing about the ones it did not.

  • Depending on the runner the test is dropped silently, or the run fails late with "cannot add a test after tests have started" — neither points at the async keyword that caused it.

  • The assertions inside the declaration protect nothing, while the file keeps reading as though they did.

  • Adding tests beside it makes the problem worse without making it visible, because they are lost the same way.

Remediation

Keep the declarations synchronous and move the asynchronous setup into a hook, which the runner does await.

// Good
describe('rates', () => {
  let rates;

  beforeAll(async () => {
    rates = await loadRates();
  });

  it('converts euros', () => {
    expect(convert(rates, 10)).toBe(12);
  });
});

References

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