How to conditionally flush a $timeout in Angular unit test

Question

I have code that is something like this:

function doThing() {
  if (invalidInput) {
    console.error(\'Invalid input.\');
    return;
  }

  $timeout(function()         


        

Answer 1

No uncertainty is welcome in unit tests, it should be predictable whether there is something to flush for $timeout or not.

In this piece of code two cases should be tested, in both $timeout shouldn't be a blackbox, it should be a stub instead (optionally a spy that wraps around the real service).

beforeEach(module('app', ($provide) => {
  $provide.decorator('$timeout', ($delegate) => {
    var timeoutSpy = jasmine.createSpy().and.returnValue($delegate);
    // methods aren't copied automatically to spy
    return angular.extend(timeoutSpy, $delegate);
  });
}));

The first is falsey invalidInput:

...
MyService.doThing();
expect($timeout).not.toHaveBeenCalled();

And the second one is truthy invalidInput:

...
MyService.doThing();
expect($timeout).toHaveBeenCalledWith(jasmine.any(Function), 1000);
$timeout.flush();
expect(MyService.doThing).toHaveBeenCalledTimes(2);

Disregarding this case, it is generally a good thing to return promises from promise-powered functions:

function doThing() {
  if (invalidInput) {
    console.error('Invalid input.');
    return;
  }

  return $timeout(function() {
    return MyService.doThing();
  }, 1000);
}

This way the callers (most likely specs) may have some control on function's asynchronous behaviour.

---

Answering the question directly, the expected way to do 'flushIfFlushable()' is

try {
  $timeout.verifyNoPendingTasks(); // just for semantics, not really necessary
  $timeout.flush();
} catch (e) {}

Which should be avoided for the reasons listed above.