Unit Tests in Angular 2

Recently at my new company, Spigit, I’ve started on working on unit testing. Now, previously I’ve done unit testing and end to end testing using NighwatchJS at Walmart Labs.
And now with my new project, I have to use Angular 2.

After working with Angular 2 for a few months now and ReactJS last year, my feelings towards the two are: ReactJS is more flexible and lightweight, and Angular 2 comes with more out of the box features. It’s kind of like the old BackboneJS vs Angular 1 argument. Do you want a more lightweight, flexible framework, or do you want to go all in with one?

With ReactJS, you only have the “view” layer and you still have to use Flux or Redux to actually make service or API calls. Then you have to add Flow for type checking.
With Angular 2, you have that all out of the box with a comprehensive library + TypeScript which has built in type checking and is ES6 natively (but not exactly the same as ES6 as I found out later on). But Angular 2 is more heavy and you might not be using its full capability, so it’s not as flexible as ReactJS. It’s just like how Angular 1.x provided everything out of the box whereas BackboneJS required you to use UnderscoreJS, jQuery etc on top of it (which some companies expanded upon more with MarionetteJS, HandlebarsJS, EpoxyJS, ThoraxJS, Lodash etc adding various capabilities onto Backbone).

Out of the two, ReactJS has a higher learning curve I feel. Having the markup in the JS files (JSX) and dealing with the component lifecycle and passing in props is a very different way of coding than the past.
Angular 2 (and Angular 4, etc) is also very different than AngularJS (that’s Angular 1.x btw), but its not quite the same chasm of difference that React is. AngularJS devs can migrate to Angular 2 fairly easily as there’s a guide for it, it still uses templates just like Backbone or AngularJS and you still have things like directives and pipes, but now everything is a component (let’s face it we live in an ES6 world now and you should be familiar with ES6 and dealing with importing/exporting components instead of the old MVC structure). Other AngularJS functions like `$scope.apply` have equivalents in Angular 2 like `changeDetectorRef.detectChanges()` But still out of the two new age popular frameworks, Angular 2 is easier to pick up. I technically prefer VueJS to either of them but it’s not quite as popular yet.

So my last 6 months with Walmart Labs I was mostly doing end to end testing using the NightwatchJS framework which uses the Selenium driver to automate browser testing. It puts less pressure on manual QA testing. We did testing on four major browsers: IE11, Firefox (last 3 versions), Chrome (last 3 versions), and Safari. We found some quirks with testing in certain browsers. For example on IE11, we would have to use clearValue twice to actually clear a value.


// For IE11
client.clearValue('input[type=text]');
client.clearValue('input[type=text]');


Which was weird, and also oddly enough on Firefox, clicking a button wouldn’t work unless the button was actually in the viewport. So we have to scroll down to it first.


// For Firefox
client.moveToElement('#main', 10, 10);
client.click("#main ul li a.first");


Very odd issues. But most people use Chrome as the standard and we only noticed the other failures since we integrated our CI with Admiral and SauceLabs.

Out of E2E testing and unit testing, Both are important, but when choosing which one to start out with, I feel unit testing is the more fundamental one to start out with. If you have a great QA team already, then you can make do without E2E testing since all it really does is automate integration testing. Unit tests also help catch regressions but on a more fundamental component level, whereas E2E catches regressions on the UI level. QAs can actually write E2E tests. But QAs usually don’t write unit tests; that’s the developers job since they know their own code the best.

ReactJS uses Mocha for unit testing (and Sinon for spies), while Angular uses Jasmine which come with their own spies. So starting out on Angular 2’s testing guide, its a big long ass intimidating page to read, and there’s tons of testing functions in there. I recommend reading the first half as the latter half are for very niche scenarios. There’s also a great plnkr link at the bottom of the page which contains ALL the unit tests in their whole, and I recommend looking at that because just showing code snippets is really not good enough. Sometimes you might be missing imports or stubs or declarations that you don’t see in the code snippets.

One of issues I ran into on the guide is using stubs vs mock classes. When we are testing components, we have to choose between using one of those if we have a function that reaches out to a service. We don’t want to call the real service. So, if we want more flexibility we can use a mock class, but the problem is Angular’s example doesn’t really work for me… when I put in the mock class as a provider using `useClass` and then using `overrideComponents`, Angular complains about it in my IDE.. I posted a question on stack overflow about it, but no one seems to reply.
So, I’m stuck using stubs instead, which is fine if the component doesn’t do too many service calls, but you lose out on the power of mock classes, but oh well. With Stubs we have to use `useValue` instead. Oh, and another gotcha I encountered… Jasmine spies by default only intercept the function but don’t call through to the real function. You have to use `spyOn(foo, ‘bar’).and.callThrough();` to actually go into the real function, which is useful when you have multiple spies on functions that call other functions.

Now I know there’s a lot of Angular 2 testing articles out there… and a lot of them have different strategies.. this is the one that worked for me…


// In addition to importing all the modules and services / providers you are using here, you need the core libraries...
import { fakeAsync, tick, async, ComponentFixture, TestBed } from '@angular/core/testing';
import { DebugElement, CUSTOM_ELEMENTS_SCHEMA, NO_ERRORS_SCHEMA } from '@angular/core';
import { By } from '@angular/platform-browser';



describe('HeaderComponent', () => {

it('should show dropdown menu when moreMenuConfig is visible', () => {
let dropdownMenu = fixture.debugElement.query(By.css('.dropdown-menu'));
expect(dropdownMenu).toBeNull();
comp.moreMenuConfig = {
visible : true,
mouseOutIntervalTime : 300,
mouseOutInterval: null,
moreMenuButtonVisible: true
};
// dropdown menu should be visible now
fixture.detectChanges();
dropdownMenu = fixture.debugElement.query(By.css('.dropdown-menu'));
expect(dropdownMenu).not.toBeNull();
});
});
});


and if you’re using Angular Bootstrap.. it actually does async stuff under the hood so you have to be careful about selecting DOM elements if they are using Bootstrap…


it('should call onScroll when scrolling on menu', async(() => {
fixture.detectChanges();
fixture.whenStable().then(() => { // wait for promise to return
fixture.detectChanges();
const menuEl = fixture.debugElement.query(By.css('.dropdown-menu'));
menuEl.triggerEventHandler('scroll', {
target: {
scrollHeight: 100,
scrollTop: 0,
clientHeight: 0
}
});
expect(comp.onScroll).toHaveBeenCalled();
expect(comp.getCommunities).toHaveBeenCalled();
})
}));


And sometimes when you are testing service calls, you also want to test for functions or code that executes in the callback of the promise as well… then you need `fakeAsync` for the job:


it('should get mini profile', fakeAsync(() => {
nameElmt.triggerEventHandler('mouseover', null); // mouseover triggers async service call
fixture.detectChanges();
tick(); // this essentially forwards the promise to the 'then' callback function
expect(userServiceStub.getMiniProfile.calls.count()).toBe(1);
}));


That’s just some sample code for testing components… now for testing services it gets more difficult since the Angular 2 testing guide doesn’t explain this very thoroughly… this is how I did it


import * as data from './data.json';


Now in TypeScript we can’t actually import json without it complaining about it missing a module definition.. unlike in native ES6. So we have to use a workaround hack .. we have to create another separate file in the same directory as the json file with the same name (including .json) so we have a file called `data.json.ts` and inside it the only content we have is

export default '';


And that’s it! Now the importing works. It’s weird but yes we have to do that until TypeScript natively supports importing JSON.

then in the test file…


describe('PageService', () => {

})));
});
});


Sometimes … there is a function that deals with DOM and things become very difficult to test with native functions like setTimeOut() for example.


keyPressHandler(event): void {
if (event.keyCode === 13 && this.searchInput.nativeElement.value) {
this.submitSearch();
}
}

clearMoreBtnTimeout() {
clearInterval(this.moreMenuConfig.mouseOutInterval);
}


In this example, its hard to test because we can’t simulate native events easily or native DOM elements that easily. Instead what we can do is pass in an optional test variable that denotes its being used for a test, and that way we can reach better code coverage without having to deal with potentially nasty DOM/event simulations.


keyPressHandler(event, test?): void {
if (event.keyCode === 13 && this.searchInput.nativeElement.value) {
this.submitSearch();
} else if (test) {
this.submitSearch();
}
}

clearMoreBtnTimeout(test?) {
// clear morebutton over timeout
if (!test) {
clearInterval(this.moreMenuConfig.mouseOutInterval);
} else {
this.moreMenuConfig.mouseOutInterval = 0;
}
}


Ok, now we can test it like this:


describe('clearMoreBtnTimeout()', () => {

And just like that, we can up our code coverage for those pesky sections of code that were hard to unit test before.

So those are my component and service tests… let me know if that helps anyone! the existing Angular 2 unit testing articles are very confusing and contradictory for me so.. this is what worked for me.