Unit testing click event in Angular

Question

I m trying to add unit tests to my Angular 2 app  In one of my components  there is a button with a  click  handler  When the user clicks the button a function is called which is defined in the  ts class file  That function prints a message in the console log window saying that the button has been pressed  My current testing code tests for printing of the console log message   describe  Component  ComponentToBeTested        gt        var component  ComponentToBeTested       beforeEach      gt            component   new ComponentToBeTested            spyOn console   log                 it  should call onEditButtonClick   and print console log        gt            component onEditButtonClick            expect console log  toHaveBeenCalledWith  Edit button has been clicked                  However  this only tests the controller class  not the HTML  I don t just want to test that the logging happens when onEditButtonClick is called  I also want to test that onEditButtonClick is called when the user clicks the edit button defined in the component s HTML file  How can I do that

User · Answer

Events can be tested using the async fakeAsync functions provided by   angular core testing   since any event in the browser is asynchronous and pushed to the event loop queue    Below is a very basic example to test the click event using fakeAsync   The fakeAsync function enables a linear coding style by running the test body in a special fakeAsync test zone   Here I am testing a method that is invoked by the click event   it  should   fakeAsync       gt        fixture detectChanges        spyOn componentInstance   method name      method attached to the click      let btn   fixture debugElement query By css  button         btn triggerEventHandler  click   null       tick       simulates the passage of time until all pending asynchronous activities finish     fixture detectChanges        expect componentInstance methodName  toHaveBeenCalled           Below is what Angular docs have to say      The principle advantage of fakeAsync over async is that the test appears to be synchronous  There is no then      to disrupt the visible flow of control  The promise-returning fixture whenStable is gone  replaced by tick        There are limitations  For example  you cannot make an XHR call from within a fakeAsync

User · Answer

My objective is to check if the  onEditButtonClick  is getting invoked when the user clicks the edit button and not checking just the console log being printed   You will need to first set up the test using the Angular TestBed  This way you can actually grab the button and click it  What you will do is configure a module  just like you would an  NgModule  just for the testing environment import   TestBed  async  ComponentFixture   from   angular core testing    describe          gt      let fixture  ComponentFixture lt TestComponent gt     let component  TestComponent     beforeEach async      gt        TestBed configureTestingModule         imports             declarations    TestComponent          providers              compileComponents   then      gt          fixture   TestBed createComponent TestComponent         component   fixture componentInstance                      Then you need to spy on the onEditButtonClick method  click the button  and check that the method was called it  should   async      gt      spyOn component   onEditButtonClick       let button   fixture debugElement nativeElement querySelector  button      button click       fixture whenStable   then      gt        expect component onEditButtonClick  toHaveBeenCalled                Here we need to run an async test as the button click contains asynchronous event handling  and need to wait for the event to process by calling fixture whenStable   Update It is now preferred to use fakeAsync tick combo as opposed to the async whenStable combo  The latter should be used if there is an XHR call made  as fakeAsync does not support it  So instead of the above code  refactored  it would look like it  should   fakeAsync      gt      spyOn component   onEditButtonClick       let button   fixture debugElement nativeElement querySelector  button      button click      tick      expect component onEditButtonClick  toHaveBeenCalled           Don t forget to import fakeAsync and tick  See also   Testing documentation What is the difference between fakeAsync and async in Angular testing

User · Answer

I m using Angular 6  I followed Mav55 s answer and it worked  However I wanted to make sure if fixture detectChanges    was really necessary so I removed it and it still worked  Then I removed tick    to see if it worked and it did  Finally I removed the test from the fakeAsync   wrap  and surprise  it worked   So I ended up with this   it  should call onClick method        gt      const onClickMock   spyOn component   onClick      fixture debugElement query By css  button    triggerEventHandler  click   null     expect onClickMock  toHaveBeenCalled          And it worked just fine

User · Answer

I had a similar problem  detailed explanation below   and I solved it  in jasmine-core  2 52  by using the tick function with the same  or greater  amount of milliseconds as in original setTimeout call   For example  if I had a setTimeout      gt         2500    so it will trigger after 2500 ms   I would call tick 2500   and that would solve the problem   What I had in my component  as a reaction on a Delete button click   delete         this myService delete this id         subscribe          response   gt              this message    Successfully deleted  Redirecting                setTimeout      gt                this router navigate    home                  2500      I wait for 2 5 seconds before redirect                   Her is my working test   it  should delete the entity   fakeAsync      gt        component id   1     preparations       component getEntity       this one loads up the entity to my component     tick       make sure that everything that is async is resolved completed     expect myService getMyThing  toHaveBeenCalledWith 1          more expects here       fixture detectChanges        tick        fixture detectChanges        const deleteButton   fixture debugElement query By css   btn-danger    nativeElement      deleteButton click       I ve clicked the button  and now the delete function is called         tick 2501      timeout for redirect is 2500 ms      lt -- solution      expect myService delete  toHaveBeenCalledWith 1          more expects here            P S  Great explanation on fakeAsync and general asyncs in testing can be found here  a video on Testing strategies with Angular 2 - Julie Ralph  starting from 8 10  lasting 4 minutes

User · Answer

to check button call event first we need to spy on method which will be called after button click so our first line will be spyOn spy methode take two arguments  1  component name 2  method to be spy i e   onSubmit  remember not use      only name required then we need to make object of button to be clicked now we have to trigger the event handler on which we will add click event then we expect our code to call the submit method once  it  should call onSubmit method       gt        spyOn component   onSubmit        let submitButton  DebugElement        fixture debugElement query By css  button type submit          fixture detectChanges        submitButton triggerEventHandler  click  null       fixture detectChanges        expect component onSubmit  toHaveBeenCalledTimes 1

[angular] Unit testing click event in Angular

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