Testing promises with Jasmine

We have been using Jasmine to test our angular code. Recently I came across a piece of code in Javascript which included a REST API call and returned a promise. The promise then had a success callback and all the rest of the play. So in this blog, I have tried to illustrate how to test a promise.

Here I have a function that returns a promise and has a success handler and failure handler. So let’s see how to test such a function:  

myFactory.getCallStatus = function() {
MyApi.getData().$promise.then(function(data) {
switch (data.status) {
case 'UPDATED':
myFactory.afterUpdate()
break;
case 'COMPLETED':
myFactory.afterCompleted();
break;
case 'FAILED':
myFactory.afterFailure()
break;
}
});
}

myFactory.afterUpdate=function(){
...
//some code here....
...
}

myFactory.afterCompleted=function(){
...
//some code here....
...
}

myFactory.afterFailure=function(){
...
//some code here....
...
}

To start testing this, create a new file named “myFactory.test.js” and initialize the factory you need to test, which in this case is “MyFactory”.

'use strict';

describe('MyFactory', function () {

var factory, $q, MyApi; // declare variables to hold reference of factory and $q service.

beforeEach(function() {
module('someModule'); // initialized module to which your factory belongs.
module(function ($provide) {
// resolve all required dependencies of factory.
$provide.factory('XYZFactory', function() {});
})

inject(function (_MyFactory_, _$q_, _MyApi_) {
factory = _MyFactory_; // inject factory for which you are writting test cases.
$q = _$q_; // As we need $q service to test function which returns promise.
MyApi=_MyApi_;
});
});

describe('Validate getCallStatus', function () {

var deferred;
var data = {'status':"UPDATED",info:'success'};

//Mocked data to resolve getData() call of MyApi .

it("Validate getCallStatus call has been completed.",function() {
deferred = $q.defer();

spyOn(MyApi, 'getData').and.callFake(function () {

//Here we will don't have mocked our getData() api call and now it returns an object of
//promise and it's not been resolved.

return {$promise:deferred.promise, $resolve:false};
});

// Now we will resolve this promise with our stubbed data.

deferred.resolve(data);
expect(MyApi.getData).toHaveBeenCalled();
expect(factory.afterUpdate).toHaveBeenCalled();
});
});

});

So that’s how we tested promise and it’s resolution. I hope this helps you in your testing.