dispatch-mail.js

const assertRejectedWith = (p, fn) => 
  Promise.all([
    assert.isRejected(p),
    p.catch(fn)
  ]);

const assertRejectedWithMsg = (p, str) =>
  assertRejectedWith(p, err => assert.deepEqual(err.message, str))

it('throws if body can\'t be found for the email type', () => {
  const payload = assoc('type', 'this-type-does-not-exist', PAYLOAD);
  return assertRejectedWithMsg(
    testDispatch(defaultTmpls, payload),
    'Body not found (type=this-type-does-not-exist, lang=en, format=html)'
  );
});