soxtoby / fakepromise

A fake Promise implementation, for testing purposes

FakePromise

A fake Promise implementation, for testing purposes.

The main difficulty with testing native promises is that their fulfillment and rejection handlers are called asynchronously, which means your test finishes before all your code has been run. Fake promises solve this by queueing up handlers, so you can decide exactly when they are executed. They also expose their current state, making them easier to assert on.

Usage

You can create a FakePromise directly, or replace native promises by calling FakePromise.replacePromise(). Native promises can be restored with FakePromise.restorePromise().

API

FakePromise supports the same API as native promises, with a few additions. If you've previously called FakePromise.replacePromise(), you can access the static functions through Promise as well as FakePromise.

FakePromise.flush()

Runs any pending fulfillment or rejection handlers. If they add more handlers to the queue, those will be run as well.

FakePromise.clear()

Clears the queue of pending handlers, so that they won't be run during the next flush().

FakePromise.defer()

Creates a new FakePromise that must be resolved or rejected manually.

FakePromise.replacePromise()

Replaces the Promise constructor with FakePromise, so any code creating Promises will create fakes instead.

FakePromise.restorePromise()

Sets Promise back to the native implementation.

#resolve(value)

Resolves the promise with the given (optional) value.

#reject(error)

Rejects the promise with the given (optional) error.

#value

Returns the value that the promise was resolved with, if it was resolved.

#error

Returns the error that the promise was rejected with, if it was rejected.

#isPending

True if the promise has been neither resolved nor rejected.

#isResolved

True if the promise has been resolved.

#isRejected

True if the promise has been rejected.