Exploring the power of "then" in AngularJS promises: Jasmine's journey

In my AngularJS controller, I have the following function:

service.getPlaceByAddress = function(address) {
    return $q(function(resolve, reject) {
        geocoder().geocode({'address': address}, function(result, status) {
            // gets called
            if (status === google.maps.GeocoderStatus.OK) {
                return resolve(result);
            }

            return reject();
        });
    });
};

I'm having trouble testing this code snippet as the then function isn't being called, even though the geocode function is definitely executed.

it('returns an error if the data service returns no results', function(done) {
    GoogleMaps.getPlaceByAddress('Testlocation').then(function() {
        done();
        // gets never called
    });

    $scope.$digest();
});

Instead of getting the expected result, I'm encountering an async timeout:

Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.

Update

Upon further investigation, when I directly return resolve, the function works as intended:

service.getPlaceByAddress = function(address) {
    return $q(function(resolve, reject) {
        return resolve();
        //geocoder()...
    });
};

It seems like the issue lies within the geocoder's callback. Oddly enough, the code functions properly in the browser but fails in the jasmine test...

Answer №1

It appears that the issue lies in your approach to testing by using a real asynchronous service instead of creating a dummy version for unit testing purposes. By implementing a dummy service that resolves promises immediately, you can simply call $scope.$digest() once in the test to activate the then() callback. However, with a genuine asynchronous call, the digest may be triggered before the remote server has a chance to respond.

To address this challenge, it is recommended to simulate the asynchronous behavior within the test environment. For example, you could replace the geocoder().geocode() function with a stub that instantly succeeds or fails when passed a specific argument like TestLocation.

Another option is to introduce a loop that waits until the request has genuinely completed. Nevertheless, relying on external services in unit tests is discouraged as these tests should be self-sufficient and not reliant on remote servers.

In reference to your query:

The blog post you referred to illustrates how to mock the geocoder function, but it only confirms that the method has been invoked without actually testing if the service promise is resolved. The spy used in the blog simply returns a value and does not activate the callback.

To enhance upon their methodology, consider utilizing a spy that triggers the callback. Since promise-related operations are asynchronous, remember to invoke $digest() to compel the promise to finalize.

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