A promise inverter for testing rejected promises with promise aware unit testing libraries.

example-1.js

import inverter from 'promise-inverter';

// Mocha style test.
it('rejects with an error', () => {
  return someRejectedPromise
    .then(...inverter)
    .then(err => assert.ok(err instanceof Error));
});

example-2.js

import { onResolve, onReject } from 'promise-inverter';

// Mocha style test.
it('rejects with an error', () => {
  return someRejectedPromise
    .then(onResolve, onReject)
    .then(err => assert.ok(err instanceof Error));
});

promise-inverter.js

export function onResolve(resolution) {
  var error = new Error('Promise should not resolve.');
  error.resolution = resolution;
  throw error;
}

export function onReject(err) {
  return err;
}

export default [onResolve, onReject];