zelda zelda - 1 month ago 8
TypeScript Question

Spec has no expectations - Jasmine testing the callback function

I have a method which is being called using a

d3 timer
. Whenever the method is called, the method emits an object with a couple of values.
One of the values increases over time. I would like to write a test to check whether the values are in the ascending order or not (i.e., increasing over time or not).

So, to tackle this, In my test, I subscribe to the event emitter and inside the subscription, I am pushing the object which I receive into a local array. And then, I am expecting the
array[i]
to be less than the
array[i+1]
. I think my logic is perfectly correct but I am not sure why I am getting an error from Jasmine saying that
the spec has no expectations
even though I have one.

Here is the code:

let x = d3.timer((elapsed) => {
this.method(); // call the function
if(elapsed >= 500) {
x.stop(); // stops the timer.
}
});

method(elapsed) {
// do something
if(elapsed > 500) {
this.output.emit({x: somevalue, y: somevalue, f: increasingvalue });
}
}


The Jasmine Spec:

it('my spec', inject([JumpService], (service: JumpService) =>{
array = [];
//service calls the method
service.output.subscribe(e => {
array.push(e);
// A console statement here will give me the length and the object pushed.
for(let i = 0; i< array.length - 1; i++) {
expect(array[i].f).toBeLessThan(array[i+1].f);
}

});

}));


Am I doing anything wrong here? How can I tackle such kind of a scenario? Please guide me in a right direction.

Thank you.

Answer Source

In general, when testing the async callback functions, it is always important to expect the outputs of the test after the promises are resolved. You can use the Angular test bed framework's tick() with the fakeAsync() or you can simply fallback to the Jasmine's general way of testing the async methods by using done()

Using done():

it('my spec', (done) => {
  array = [];
  service.output.subscribe(e => {
   array.push(e);
   for(let i = 0; i< array.length - 1; i++) {
    expect(array[i].f).toBeLessThan(array[i+1].f);
   }
   done();
  });
});

Hope this answer helps.

Note: I didn't had great luck with the fakeAsync() and tick(), so I am not including it in the answer. Sorry about that.