Unit test CHILD component from PARENT component’s test case

Here are some ways to get a child component in a parent test case in Angular:

1. Using fixture.debugElement.query():

const childDebugElement = fixture.debugElement.query(By.directive(ChildComponent));
const childComponent = childDebugElement.componentInstance;

This method uses the debugElement property of the fixture to query for the child component.

2.Using fixture.debugElement.queryAll():

const childDebugElements = fixture.debugElement.queryAll(By.directive(ChildComponent));
const childComponents = childDebugElements.map(de => de.componentInstance);

This method uses the queryAll method to retrieve an array of debug elements that match the child component directive.

3.Using fixture.nativeElement.querySelector():

const childElement = fixture.nativeElement.querySelector('app-child');
const childComponent = fixture.debugElement.query(By.css('app-child')).componentInstance;

This method uses the nativeElement property of the fixture to query for the child component element, and then uses the debugElement property to retrieve the component instance.

4.Using a test double or spy:

const childComponentSpy = jasmine.createSpyObj('ChildComponent', ['methodName']);
TestBed.configureTestingModule({
  declarations: [ParentComponent],
  providers: [{ provide: ChildComponent, useValue: childComponentSpy }]
});

This method creates a test double or spy for the child component, allowing you to test the parent component’s interactions with the child component without actually rendering the child component.

5.Using ViewChild:
// parent.component.ts

@ViewChild(ChildComponent) childComponent: ChildComponent;

// parent.component.spec.ts

const childComponent = fixture.componentInstance.childComponent;

This method uses the ViewChild decorator to retrieve a reference to the child component instance in the parent component.

These are just a few examples of how you can get a child component in a parent test case in Angular. The best approach will depend on your specific testing needs and requirements.