Creating spec.ts files for components by hand: A guide

Currently, I am facing an issue where the automatic generation of spec.ts files has been disabled by the developers when they created the components. To address this, I manually created the spec.ts files by copying over an existing one into each component, with the only difference being the name of the component.

import { ComponentFixture, TestBed } from '@angular/core/testing';

import { NavMenuComponent } from './nav-menu.component';

describe('NavMenuComponent', () => {
  let component: NavMenuComponent;
  let fixture: ComponentFixture<NavMenuComponent>;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ NavMenuComponent ]
    })
    .compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(NavMenuComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

Upon running 'npm run test', the tests failed for nearly every component. I suspect that there may be additional steps required beyond just creating the spec.ts file and adding the code above. The error message generated by npm run test is quite lengthy and seems to indicate that I am importing something that does not exist, but I am unsure how to resolve this issue:

Chrome 85.0.4183.121 (Mac OS 10.15.7) SelectiveComponent should create FAILED
NullInjectorError: R3InjectorError(DynamicTestModule)[SearchService -> HttpClient -> HttpClient]: 
  NullInjectorError: No provider for HttpClient!
error properties: Object({ ngTempTokenPath: null, ngTokenPath: [ 'SearchService', 'HttpClient', 'HttpClient' ] })
NullInjectorError: R3InjectorError(DynamicTestModule)[SearchService -> HttpClient -> HttpClient]: 
  NullInjectorError: No provider for HttpClient!
    at NullInjector.get (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:915:1)
    at R3Injector.get (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:11076:1)
    ...

If anyone has insights or suggestions on how to resolve this issue, any help would be greatly appreciated!

Answer №1

This error indicates that your NavMenuComponent relies on a SearchService service which in turn is dependent on the HttpClient service.

To address this, you can create a mock for the dependency using jasmine. In my testing experience, I find it beneficial to mock direct dependencies when testing components. By mocking the SearchService calls, you can effectively test the component behavior.

describe('NavMenuComponent', () => {
  let component: NavMenuComponent;
  let fixture: ComponentFixture<NavMenuComponent>;
  
  // create a mock of the http client
  // the second param will be a list of functions your service has to offer
  let mockSearchService = jasmine.createSpyObj('searchService', ['search']);

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ NavMenuComponent ],
      providers: [
        // provide your obj in place of the actual SearchService
        {provide: SearchService, useValue: mockSearchService}     
      ]
    })
    .compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(NavMenuComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

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