Using Jasmine's done() Callback for Asynchronous Tests

When to use done()

To test asynchronous code in Jasmine, pass a done callback to the test function and invoke it when the async work finishes. Jasmine will not proceed to the next spec until done is called (or the default timeout expires).

Basic syntax

it('fetches user data', function(done) {
  // Assume fetchUser returns a Promise
  fetchUser(123)
    .then(user => {
      expect(user.id).toBe(123);
      done(); // signal success
    })
    .catch(err => {
      done.fail(err); // signal failure with error details
    });
});

How Jasmine waits for done()

When the test function receives a done argument, Jasmine changes its completion criteria:

• The spec is considered pending until done is invoked.
• If done is not called within the default timeout (5 seconds), Jasmine fails the spec with a timeout error.
• Calling done more than once, or after Jasmine has already moved on, throws an error to prevent false‑positive passes.

Limits and common mistakes

• Omitting the parameter – If you write it('test', function() { ... }) without done, Jasmine treats the test as synchronous. Any asynchronous work will likely finish after the spec ends, causing a silent pass or a timeout that is hard to trace.
• Using arrow functions – Arrow functions lexically bind this and do not alter the arguments object. Writing it('test', () => { ... }) prevents Jasmine from injecting a done callback, leading to the same issue as omitting the parameter.
• Mixing done() with async/await – Returning a promise or using async already signals completion. Adding a done call in addition can cause race conditions; the test may finish twice, triggering Jasmine’s error about multiple calls.
• Failing to handle errors – Forgetting to call done.fail in a .catch block leaves Jasmine waiting for done that never arrives, resulting in a timeout.

To verify behavior, create a fresh Node project, install Jasmine (npm install --save-dev jasmine), run jasmine init, add a spec file with the example above, and execute jasmine. Observe a passing test when the promise resolves, a failure when it rejects, and a timeout when done is omitted or called twice.