This rule raises an issue when a test or lifecycle-hook callback is declared async and also accepts a completion callback such as done.

Why is this an issue?

Asynchronous tests and hooks must use a single completion style.

In Jest, Mocha, and Jasmine, a test or hook can finish in one of two ways:

• callback style: call the completion callback
• promise style: return a promise, including by declaring the callback async

A callback that does both mixes these contracts. The framework has to choose between the callback and the returned promise, which is unsupported or ambiguous. Depending on the framework and the code path, this can fail immediately, hang until timeout, or report failures in a confusing way.

Choose the style that matches the body of the callback:

• If the callback already awaits or returns a promise, remove the completion callback and rely on async or the returned promise.
• If the callback is built around a callback-based API, keep the completion callback and make the function synchronous.

Exceptions

This rule does not raise on modifier-based skipped tests such as it.skip(…​) or test.skip(…​).

Code examples

Noncompliant code example

it("loads the configuration", async done => { // Noncompliant: this test uses both promise completion and the "done" callback
  const config = await loadConfig();
  expect(config.port).toBe(3000);
  done();
});

Compliant solution

it("loads the configuration", async () => {
  const config = await loadConfig();
  expect(config.port).toBe(3000);
});

Noncompliant code example

beforeEach(async done => { // Noncompliant: this hook is callback-based, so "async" is misleading
  connectToDatabase(error => {
    done(error);
  });
});

Compliant solution

beforeEach(done => {
  connectToDatabase(error => {
    done(error);
  });
});

Resources

Documentation

• Jest Documentation - Testing Asynchronous Code
• Mocha Documentation - Asynchronous Code
• Jasmine Documentation - Testing Async Code
• Jasmine Documentation - FAQ: callback and promise