Angular 单元测试 - 更改单个测试的模拟服务类的方法返回

Question

在我的单元测试中，我有一个正在使用的模拟服务类MockWorkflowService，它有一个方法getActiveTask。大部分测试都需要此方法的默认功能，但是有几个测试我需要重写此方法并让它返回 null。但是我这样做没有任何运气（请参阅代码块底部的测试）：

class MockWorkflowService {
  getActiveTask() {
    return new Action({
      name: 'test',
      value: 4
    })
  }
}

describe('MyComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [
        MyComponent
      ],
      providers: [
        TranslateService,
        { provide: WorkflowService, useClass: MockWorkflowService }
      ]
    })
      .compileComponents();
  }));

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

  it('should ...', () => {
    // TRYING TO DO SOMETHING LIKE
    MockWorkflowService.getActiveTask = () => null;
  });

})

我尝试执行 MockWorkflowService.prototype.getActiveTask = () => null，它适用于我想要覆盖它的单个测试，但随后该方法对所有剩余测试返回 null。

任何帮助将不胜感激，谢谢。

Answer 1

当您只想为该特定测试覆盖时，您需要执行此操作。您正在做的是覆盖该服务的所有实例，这是错误的。你可以按照这个：

// Define the service here: 
describe('MyComponent', () => {
  let workflowService: WorkFlowService // Add this line
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [
        MyComponent
      ],
      providers: [
        TranslateService,
        { provide: WorkflowService, useClass: MockWorkflowService }
      ]
    })
      .compileComponents();
  }));

// In before each, create an instance of the service
 beforeEach(() => {
    fixture = TestBed.createComponent(MyComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
    workFlowService = TestBed.get(WorkflowService); // Add this line
    // TestBed.get should be TestBed.inject if you're using Angular 9+
  });


it('should ...', () => {
  // Spy on the service and return null
  // This will call the mock service class and return null for this test case

  spyOn(workFlowService, 'getActiveTask').and.returnValue(null);
  component.yourComponentMethodName();
  expect(component.yourComponentMethodName).toHaveBeenCalled();
});