Error when writing tests for the auth guard: The '_Router' token injection failed. 'inject()' function must be called from an injection context

[thelongshot]

When we rewrote the guard in the 'new' way, we found that one of our tests doesn't work anymore. It is mainly because of this line at the end of the guard. It mostly follows the code in the documentation.

// If not valid, redirect to the welcome screen
return inject(Router).createUrlTree(['/welcome']);

The test looks like this:

const fakeUrlTree = { toString: () => '/welcome' } as unknown as UrlTree;

it('should redirect when required role not present', async() => {
const activatedRoute = jasmine.createSpyObj<ActivatedRouteSnapshot>('activatedRoute', {}, { data: { roles: [ Role.Admin ] }} )
const routerState = jasmine.createSpyObj<RouterStateSnapshot>('routeState', {}, {url: '/test'})

await Testbed.runInInjectionContext(async () => {
expect await guard(activatedRoute, routerState)).toBe(fakeUrlTree);
})
})

Unfortunately, this fails with "The '_Router' token injection failed. 'inject()' function must be called from an injection context". Testbed.runInInjectionContext is supposed to take care of that, but seems to have issues with the async method of the guard. I've tried the call with and without the await before guard, with no difference. I'm kinda baffled at what is going on here and how to get this test running again.

I had looked at the test in gitlab, but that doesn't test the logic of the guard. Just a mock guard and checking the inputs and outputs. Is there some way to test when it falls out?

[mauriciovigolo]

Thank you for providing the test code. The guard implementation is correct — the issue is with the test setup.

Your guard uses:

return inject(Router).createUrlTree(['/welcome']);

TestBed.runInInjectionContext() is required (and you are using it), but it only creates a DI context. The Router is not provided in your test, which causes:

The '_Router' token injection failed

Also, your assertion:

expect(await guard(activatedRoute, routerState)).toBe(fakeUrlTree);

compares object identity, but createUrlTree() returns a new UrlTree instance. It will fail unless you mock createUrlTree.

Here’s a probably working example with a mocked Router:

const fakeUrlTree = { toString: () => '/welcome' } as UrlTree;

beforeEach(() => {
  TestBed.configureTestingModule({
    providers: [
      { provide: Router, useValue: { createUrlTree: () => fakeUrlTree } }
    ]
  });
});

it('should redirect when required role not present', async () => {
  const activatedRoute = jasmine.createSpyObj<ActivatedRouteSnapshot>(
    'activatedRoute', {}, { data: { roles: [Role.Admin] } }
  );
  const routerState = jasmine.createSpyObj<RouterStateSnapshot>(
    'routerState', {}, { url: '/test' }
  );

  await TestBed.runInInjectionContext(async () => {
    const result = await guard(activatedRoute, routerState);
    expect(result).toBe(fakeUrlTree);
  });
});

[mauriciovigolo]

I will close this issue, as it is not a bug in the library. If needed, feel free to open it again. Thank you, @thelongshot.

[thelongshot]

I mostly have it the way you have it written here. I made some minor changes to the Router provider declaration, but it didn't make any difference. I still get the error.

…

On Tue, Dec 30, 2025 at 12:56 PM Mauricio Vigolo ***@***.***> wrote: Closed #690 <#690> as completed. — Reply to this email directly, view it on GitHub <#690 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA4YIUNRP7CU4ETGFNDVH6D4EK4E3AVCNFSM6AAAAACQIMTQSOVHI2DSMVQWIX3LMV45UABCJFZXG5LFIV3GK3TUJZXXI2LGNFRWC5DJN5XDWMRRG44TONRZHE2TGMI> . You are receiving this because you were mentioned.Message ID: ***@***.*** com>

[mauriciovigolo]

Hi @thelongshot, could you prepare a reproducible example of the error (CodePen or a similar tool is fine)?
Thanks!

[thelongshot]

Here is my stackblitz reproducing the error. https://stackblitz.com/edit/stackblitz-starters-dkkfpndz?file=src%2Fguard%2Fapp.guard.spec.ts&view=editor Run ng test and you can see the error. Jason

…

On Thu, Jan 1, 2026 at 4:29 AM Mauricio Vigolo ***@***.***> wrote: Reopened #690 <#690>. — Reply to this email directly, view it on GitHub <#690 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA4YIUJILQNVGEMTQS7XEN34ETSHDAVCNFSM6AAAAACQIMTQSOVHI2DSMVQWIX3LMV45UABCJFZXG5LFIV3GK3TUJZXXI2LGNFRWC5DJN5XDWMRRHAYTOMJUGUYDGMA> . You are receiving this because you were mentioned.Message ID: ***@***.*** com>