Using expect() within the .then() function when writing Jasmine unit tests for AngularJS

I'm currently struggling with the .then() function while trying to implement Jasmine unit testing. Here is the code that's giving me trouble:

describe("getBuilding", function () {
  it("checks getBuilding", function () {
    var id_building = 4;
    LocalDB.getTestData();
    LocalDB.getBuilding(id_building).then(function (result) {
      expect(result.name).toMatch("Something");
    });
  });
});

In this scenario, the result variable seems to have the correct value in the then() function, but the expect statement doesn't seem to work properly. Even if I change "Something" to "something else," the test still passes when it shouldn't.

I attempted to resolve the issue by modifying the code like so:

describe("getBuilding", function () {
  it("checks getBuilding", function () {
    var id_building = 4;
    LocalDB.getTestData();
    expect(LocalDB.getBuilding(id_building).name).toMatch("Something");
  });
});

or

describe("getBuilding", function () {
  it("checks getBuilding", function () {
    var finalResult;
    var id_building = 4;
    LocalDB.getTestData();
    LocalDB.getBuilding(id_building).then(function (result) {
      finalResult=result.name;
    });
    expect(finalResult).toMatch("Something");
  });
});

However, in both cases, the value being matched turns out to be undefined. Would appreciate any advice on how to tackle this issue. Thank you!

Answer №1

It's possible that your 'then()' function is not being executed at all, as promises are resolved asynchronously. To ensure proper execution of your tests, make sure the promises are resolved before exiting or utilize jasmine async to have jasmine wait for the async method to resolve before proceeding to the next test.

In unit testing with promises, it's often necessary to manually inform the AngularJS lifecycle when it's time for promises to be resolved.

You can try adding the $rootScope dependency and invoking $rootScope.$digest() at the end of your test like below:

describe("getBuilding", function () {
  it("checks getBuilding", function () {
    var id_building = 4;
    LocalDB.getTestData();
    LocalDB.getBuilding(id_building).then(function (result) {
      expect(result.name).toMatch("Something");
    });
    $rootScope.$digest();
  });
});

If this approach doesn't work on its own, consider using Jasmine Async as shown below:

describe("getBuilding", function () {
  it("checks getBuilding", function (done) {
    var id_building = 4;
    LocalDB.getTestData();
    LocalDB.getBuilding(id_building).then(function (result) {
      expect(result.name).toMatch("Something");
      done();
    }, function(){
      done.fail('The promise was rejected');
    });
    $rootScope.$digest();
  });
});

The Jasmine Async method utilizing done is a more robust test, as it will fail if the promise is rejected. The first method may pass silently even if the promise is rejected. However, if you are confident that the promise will always resolve, the initial approach could suffice for your situation.

Answer №2

After reading through this link on Jasmine's asynchronous support, it becomes clear that Jasmine does offer support for async methods. The main issue often encountered is asserting values before the async call has completed, resulting in failed asserts due to missing data.

One possible solution, as suggested in the provided link (although not tested personally as I am not very familiar with Jasmine), is to structure the code similar to the following example:

describe("getBuilding", function () {
  it("checks getBuilding", function () {
    var id_building = 4;
    LocalDB.getBuilding(id_building).then(function (result) {
      expect(result.name).toMatch("Something");
      done();
    });
  });
});

Answer №3

Make sure to fulfill the promise.

fulfill BuildingDB.fetchBuilding(building_id)
    .then(function (output) {
       verify(output.title).toConformTo("Certain Criteria");
    });

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