Angular5/Karma is raising the error message "selector is not a recognized element"

I am encountering a small issue with my component. While everything seems to be working fine in my browser without any errors, the Karma debugger is throwing some errors that I would like to resolve for clarity.

Error:

Failed: Template parse errors:
'dj-menu' is not a known element:
1. If 'dj-menu' is an Angular component, then verify that it is part of this module.
2. If 'dj-menu' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

The <dj-menu> selector is being used in app.component.html.

menu.component.ts

import {Component, OnInit} from '@angular/core';

@Component({
    selector: 'dj-menu',
    template: `<nav>
                        <button mat-button routerLink="/login" routerLinkActive="active">Login</button>
                        <button mat-button routerLink="/register" routerLinkActive="active">Register</button>
                        <button mat-button routerLink="/profile" routerLinkActive="active">Profile</button>
                        <button mat-button routerLink="/radio">Radio</button>
                   </nav>
`,
    styleUrls: ['./menu.component.scss']
})
export class MenuComponent implements OnInit {
    {...} // only an empty constructor and ngOnInit()
}

I have a MenuComponent declared in declarations within the @NgModule of app.module.ts.

While the component works well in the browser, there are issues in the Karma debugger. I have tried several solutions found online, such as If '<selector>' is an Angular component, then verify that it is part of this module, but none have resolved the problem yet.

Your assistance is much appreciated, thank you.

Answer №1

When testing a parent component, it's important to stub out any child components that are used within it. For instance, if I have two components - one named app and the other named dj-menu - I should create a mock version of dj-menu for testing purposes within the app component test using code like this:

@Component({
selector: 'dj-menu',
  template: '<h1> Some test </h1>'
})

class DjMenuComponentStub{
}

Here is an example of how my app component looks, which includes the use of dj-menu:

@Component({
selector: 'app',
  template: '<dj-menu></dj-menu>'
})

class AppComponent{
}

Since angular is not aware of the dj-menu component during testing, you need to explicitly declare the use of the stub component by including it in the TestBed configuration:

TestBed.configureTestingModule({
      declarations: [ DjMenuComponentStub ]
})

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