Angular + Karma: Testing async functions

Question

I have an angular service that does some async stuff (based on timers). One of the things you can do with a timer is define a 'handler' that fires when the timer expires (as in this pseudo-code):

flag = false;
timer = new Timer(1000); // ms
timer.handler = function () { flag = true };

In this trivial case, the timer would set flag to true after 1 second. How do I unit test this with Angular/Karma/Jasmine?

From reading the docs, I would have expected this to work:

... 
flag = false;
timer = new Timer(1000);
timer.handler = function () { flag = true };
expect(flag).toBe(false);
sleep(2)
expect(flag).toBe(true);
...

Rather than being morally upright, that test decided to fail with this:

ReferenceError: Can't find variable: sleep

After some reading, apparently I can't use angular-scenario with Jasmine. Ok, I'm cool with that.

UPDATE : Per the comments, I tested my "working" settimeout method. It doesn't ever get called.

~~So this works:~~

... 
flag = false;
timer = new Timer(1000);
timer.handler = function () { flag = true };
expect(flag).toBe(false);
setTimeout(function () { expect(flag).toBe(true) }, 2000);
...

~~But feels a little weird.~~

Question: Is there a better way?

Fun Trivia: Yep, I know about $timeout. I have Very Good Reasons(TM) for doing the things I did deep in the code mines, away from the light of day =)

if you were to use the $timeout you were able to call $timeout.flush(); with this you may test the pre timer conditions and the post timer conditions. But you do not want it :) — michael
– michael, Commented Jan 15, 2014 at 19:59
@rdodev: Well, I don't know if this is why it felt weird before, but I just tested and the expect() inside the timeout doesn't actually get called (I set the time to 10 seconds and reran the test, but it finished almost immediately). — Sir Robert
– Sir Robert, Commented Jan 15, 2014 at 20:01
@Michael: My timer has a method equivalent to flush(), but that's not what I'm trying to test. — Sir Robert
– Sir Robert, Commented Jan 15, 2014 at 20:01
In your last code snippet, when does the Timer() get triggered? At instantiation time? — rdodev
– rdodev, Commented Jan 15, 2014 at 20:04

Sir Robert · Accepted Answer · 2014-01-15 20:49:42Z

12

Jasmine has a way to do async testing using waits() or waitsFor() and runs(). Look here.

Code would be something like:

... 
flag = false;
timer = new Timer(1000);
timer.handler = function () { flag = true };
expect(flag).toBe(false);
waitsFor( function() {
  return flag;
}, "timer ran");
runs( function() {
  expect(flag).toBe(true);
});
...

Note from OP

This is the right solution, so I marked it as accepted. I actually ended up implementing a sleep-like method based on this solution, and wanted to share in case it was helpful to others.

In the test file:

function loiter(ms) {
  var loiter = true;
  setTimeout(function () {loiter = false}, ms);
  waitsFor( function () {return !loiter}, "Loitered too long", ms + 50); 
}

it("should ...", function () {
  flag = false;
  timer = new Timer(1000);
  timer.handler = function () {flag = true};
  setTimeout(function () {expect(flag).toBe(true)}), 1100);

  loiter(1200);
})

I hope this is useful! I'll leave it as an exercise for the reader to figure out why I did it this way =)

edited Jan 15, 2014 at 20:49

Sir Robert

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answered Jan 15, 2014 at 20:21

Alan Yackel

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3 Comments

Sir Robert Over a year ago

This is the right answer. Michael answered first in the comments above, but if he doesn't provide an answer soonishly, I'll accept yours as correct. Thanks =)

John Haugeland Over a year ago

"I'll leave it as an exercise for the reader to figure out why I did it this way =)" It would be nice if you'd finish explaining.

Thomas Kekeisen Over a year ago

setTimeout(function () {expect(flag).toBe(true)}), 1100); should be setTimeout(function () {expect(flag).toBe(true)}, 1100); - works great! :-)

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