How do I debug a "[object ErrorEvent] thrown" error in my Karma/Jasmine tests?

I have several failing tests that only output [object ErrorEvent] thrown. I don't see anything in the console that helps me pinpoint the offending code. Is there something I need to do to track these down?

[EDIT]: I'm running Karma v1.70, Jasmine v2.7.0

> FYI: you can find the exact error thrown just by open DevTools Console once your tests are running.

As a quickfix you can try to run your tests without sourcemaps:

CLI v6.0.8 and above
--source-map=false

CLI v6.0.x early versions
--sourceMap=false

CLI v1.x
--sourcemaps=false

> Shortcut ng test -sm=false might also work

There is an open issue on that https://github.com/angular/angular-cli/issues/7296

UPDATE: I had that issue as well, so I just migrated to the latest cli and make sure that all packages are updated in package.json also I fully reinstalled the node_modules so now the issue has gone.

If sourcemap=false doesn't help, try to

1. open your browser running the tests
2. click debug button
3. open the console

The error will be there

Try if you get a more descriptive error message by running the test from the terminal, like this:

ng test -sm=false

In your test, you can replace

it('should...')

with

fit('should...') 

Now only tests preceded by fit will run. To leave the browser open after running the test, run the test like this:

ng test -sm=false --single-run false

---

Personally, I have encountered this error twice. Both were only triggered when calling fixture.detectChanges().

The first time, I solved it by using string interpolation more safely in my .html file.

Unsafe example:

<p>{{user.firstName}}</p>

Safe(r) example (note the question mark):

<p>{{user?.firstName}}</p>

The same may apply to property binding:

<p [innerText]="user?.firstName"></p>

---

The second time, I was using a DatePipe in my .html file, but the mock property that I used it on was not a date.

.html file:

<p>{{startDate | date: 'dd-MM-yyyy'}}</p>

.ts (mock-data) file (wrong):

let startDate = 'blablah';

.ts (mock-data) file (correct):

let startDate = '2018-01-26';

This is because the jasmine framework can not handle the ErrorEvent type so it does not extract the error message and calls error.toString() on that object instead.

I just filed an issue at jasmine repo https://github.com/jasmine/jasmine/issues/1594

As long as it is not fixed, you can temporarily patch your installed jasmine package in the node_modules folder. In my case it is

node_modules/jasmine/node_modules/lib/jasmine-core/jasmine.js

and then change the implementation of the ExceptionFormatter from this

if (error.name && error.message) {
    message += error.name + ': ' + error.message;
} else {
    message += error.toString() + ' thrown';
}

to this

if (error.name && error.message) {
    message += error.name + ': ' + error.message;
} else if (error.message) {
    message += error.message;
} else {
    message += error.toString() + ' thrown';
}

It helps to identify the issue.

For me it was related to having a promise resolved in the ngOnInit of a component. I had to use async, fakeAsync and tick as well as stubbing out the async service with spyOn

beforeEach(async(
  //... initialise testbed and component
))
beforeEach(fakeAsync(
  // ... setup mocks then call:
  component.ngOnInit()
  tick()
  fixture.detectChanges()
))

https://stackoverflow.com/questions/46914105/angular-how-to-unit-test-component-with-asynchronous-service-call

TL;DR: It may be related to testing routing.

I'm getting [object ErrorEvent] thrown too. An hour later, traced it to one line of code.

this.username = this.userService.getUser(this.route.snapshot.paramMap.get('id'))[0];

The problem lies with the test environment attempting to evaluate this.route.snapshot.paramMap.get('id').

If I replace it with 0, [object ErrorEvent] thrown goes away.

My userService has a user like so:

public users = [ ["admin", "First name", "Surname", etc... ] ].

So 0 just gets this user, at index 0.

Otherwise when normally running my app, this.route.snapshot.paramMap.get('id') is evaluated when the user selects a user to edit from my table of users.

So in my HTML, *ngFor="let user of users; index as i" loops to display all the users then routerLink="/edit/{{i}}" so you can click on edit buttons for each user, which when clicked go to e.g. http://localhost:4200/edit/0 to edit the aforementioned admin user's details.

what about cleaning after each test case:

  afterEach(() => {
    TestBed.resetTestingModule();
  })

For me, this was caused by not defining an error handler for an api I was subscribed to.

My fix just involved adding the block of code to handle (err) below:

it('reports an error to subscribers of api calls if not authenticated', (done) => {
    let obsDataFound = dataService.find(1);
    obsDataFound.subscribe((app) => {
        // not expecting this block to be called
        done();
    }, (err) => {
        // This is the err block that I added that solved the problem
        expect(true).toBeTruthy();
        done();
    });

    let testRequest = httpMock.expectOne({method: 'GET'});
    const mockErrorResponse = { status: 401, statusText: 'Unauthorized test status message' };
    testRequest.flush(appTest, mockErrorResponse);
});

I had the same problem. One way this error happens is when you try to access anything null or undefined in template. Make sure you have safety checking on those variable.

For example this will throw [object: ErrorEvent] when config is undefined on component load.

template.html

<div *ngIf="config.options">
   .....
   ......
</div>

Do this instead

<div *ngIf="config?.options">
   .....
   ......
</div>

What can help is, if you have the Chrome window open for your Karma test runner, to open the developer tools and check the console there. For me, this helped me to find out that the app could not use the Array.findIndex method on an undefined array (because the data structure was organized by a date string, such as data[2018][3][28], and I happened to be pointing to the wrong date), but yet instead of just stopping at the error, the test kept running.

You may have a race or an async test that isn't set up quite right or is used incorrectly. I would assume that the debug case needs to be fixed and ignore that the command line passes. Just keep refreshing the karma test runner (browser) in case the error [object ErrorEvent] thrown appears intermittently, then make sure you have implemented the async condition correctly.

Hopefully this works.

For me the issue was that I had a test where I was accidentally using the auth0-lock library.

It appeared to be an async problem, because after I added enough its in one of my component specs, I was able to get a usable error message which pointed to a file and line within that file (it was related to paramMap.

In the spec that tested ParamMap, I just added:

  describe('this test', () => {
    it('will succeed', () => {
      expect(true).toBeTruthy();
    });

    it('will succeed', () => {
      expect(true).toBeTruthy();
    });

    it('will succeed', () => {
      expect(true).toBeTruthy();
    });

    it('will succeed', () => {
      expect(true).toBeTruthy();
    });
  });

> [object ErrorEvent] thrown

This error shows that you have something undefined. The easiest way to debug it from my experience is :

it('should create', () => {
    console.log(component);
    // You can check in the browser log which property is undefined
    });

In my case the problem was with the service, as one of the object wil be undefined during tests running.

Service code sample was something like below access to dom,

  const elem = this.document.querySelector(element) as HTMLElement;
  elem.scrollIntoView({param1: ''});

The specs referring to this service were failing with the error '[object ErrorEvent] thrown'.

I mocked my service object inside all the specs which were referring to this and the issue got resolved.

Mock service

class MockService {
serviceMethod(div) : void {
  testElement = document.querySelector('div') as HTMLElement;
  return testElement;
  } 
}

And use this mock service object in providers as below,

beforeEach(async(() => {

TestBed.configureTestingModule({
  declarations: [Component],
  providers: [
     { provide: Service, useClass: MockService },
    ],
})
  .compileComponents();
}));

I was using a proxy in my application defined in proxy.conf.json like:

'/api': { 'target': 'some path', 'changeOrigin': false }

Because Karma wasn't aware of this proxy, it kept trowing errors in the console that the API endpoint could not be found. So after looking in the Karma documentation, I found out that what I could do was to add the "proxies" property in karma.conf.js with the same object from the proxy.conf.json:

proxies: { '/api': { 'target': 'some path', 'changeOrigin': false }}

The error in the console was gone, and the [object errorEvent] was no longer thrown.

In the end, what can worked for me:

    TestBed.resetTestingModule();
  })