Unit testing ember-concurrency tasks and yields

Question

We have a lot of code in our project that isn't covered because of ember concurrency tasks.

Is there a straightforward way of unit testing an controller that contains something like the following:

export default Controller.extend({
    updateProject: task(function* () {
        this.model.project.set('title', this.newTitle);
        try {
            yield this.model.project.save();
            this.growl.success('success');
        } catch (error) {
            this.growl.alert(error.message);
        }
    })
});```

Answer 1

You can unit test a task like that by calling someTask.perform(). For the given task you can stub what you need to in order to test it thoroughly:

test('update project task sets the project title and calls save', function(assert) {

  const model = {
    project: {
      set: this.spy(),
      save: this.spy()
    }
  };
  const growl = {
    success: this.spy()
  };

  // using new syntax
  const controller = this.owner.factoryFor('controller:someController').create({ model, growl, newTitle: 'someTitle' });

  controller.updateProject.perform();

  assert.ok(model.project.set.calledWith('someTitle'), 'set project title');
  assert.ok(growl.success.calledWith('success'), 'called growl.success()');
});

This is using spies from sinon and ember-sinon-qunit to access sinon from a test context, but these are not necessary for unit testing. You could stub the model and services, etc. with assertions instead of spies:

const model = {
  project: {
    set: (title) => {
      assert.equal(title, 'someTitle', 'set project title');
    },
    save: () => {
      assert.ok(1, 'saved project');
    }
  }
};

To test the catch you can throw from your stubbed model.project.save() method:

const model = {
  project: {
    ...
    save: () => throw new Error("go to catch!")
  }
};