How to test function inside ngOnInit

Question

My component class is simple. It takes an input from parent component and based on that input it resolves a parameter from an ENUM inside the ngOnInit
My Component class:

export class TestComponent implements OnInit {
@Input() serviceType: string;
serviceUrl : string;

ngOnInit() {
        this.findServiceType();
    }
    
findServiceType= () => {
        if (this.serviceType) {
            if (this.serviceType === 't1') {
                this.serviceUrl = TestFileEnumConstants.T1_URL;
            }else if (this.serviceType === 't2') {
                this.serviceUrl = TestFileEnumConstants.T2_URL;
            }
        }
    }
    
 }

My Test Class:

describe('testcomponent', () => {

    let component: TestComponent;
    let fixture: ComponentFixture<TestComponent>;
    let mockService = <Serv1>{};
    
    beforeEach(() => {
        TestBed.configureTestingModule({
            imports: [FormsModule],
            declarations: [
                TestComponent, TestChildComponent],
            providers: [
                { provide: MockService, useValue: mockService }
                ]
        });
        fixture = TestBed.createComponent(TestComponent);
        component = fixture.componentInstance;
    });
    
    it('should create testcomponent', () => {
        expect(component).toBeDefined();
    });
    
     describe('testType1',  () => {
        beforeEach( () => {
            spyOn(component, 'findServiceType');
            
        });
        it('should correctly wire url based on type1', () => {
            component.serviceType = 'type1';
            fixture.detectChanges(); 
            expect(component.findServiceType).toHaveBeenCalled();
            expect(component.serviceUrl).toBe(TestFileEnumConstants.T1_URL)
        });
    });
    
    }

The issue is serviceUrl is not getting poluplated because 'serviceType' - the input is coming as undefined even after change detection is called.

Answer 1

The issue was because of a SpyOn statement in the beforEach() segment. Since the mock function is not returning any data, the return value keep on getting undefined. The problem statement is given below, I have to comment the spyOn statement:

beforeEach( () => {
            // spyOn(component, 'findServiceType');
            
        });

Removed this function and worked fine.