typescript - 在 Jest 中，我如何对订阅 observable 的方法进行单元测试

Question

我的组件中有各种方法订阅注入(inject)依赖项中的方法，这些方法返回可观察对象。

我想编写 Jest 单元测试以确保当这些可观察对象返回/错误时，我的方法会做正确的事情。

在下面的示例中，我正在尝试编写一个测试来检查 doAThing已经开除了。以下测试均无效。他们都因错误而失败，例如

'returnMyObservable.subscribe is not a function'.

// Example method to test component 
public testFunction (): void {
    this.myService.returnMyObservable.subscribe(
        ( value ) => this.doAThing( value )
    )
}

describe( 'myComponemt', () => {

    let fixture;
    let myServiceMock;

    beforeEach( () => {
        myServiceMock = {
            returnMyObservable: fn()
        }

        fixture = new myComponent( myServiceMock );
    });


    // 1) I have tried mocking with a returned value
    it ( 'should call do a thing when value is returned', () => {
        myServiceMock.returnMyOnservable.mockReturnValue( true );

        fixture.testFunction();

        expect( fixture.doAThing ).toHaveBeenCalled();
    });

    // 2) I have tried returning an observable
    it ( 'should call do a thing when value is returned', () => {
        myServiceMock.returnMyOnservable.mockReturnValue( of( true ) );

        fixture.testFunction();

        expect( fixture.doAThing ).toHaveBeenCalled();
    });

});

Answer 1

我还有一些其他错误掩盖了我的测试实际出了什么问题——我发现测试上述功能的最佳方法是:

describe( 'MyComponent', () => {
    let fixture;
    let myServiceMock;

    beforeEach( () => {
        myServiceMock = {
            returnMyObservable: jest.fn()
        }

        fixture = new MyComponent( myServiceMock );
    });

    it ( 'should call doAThing when value is returned', () => {
        const doAThingSpy = jest.spyOn( fixture, 'doAThing' );
        myServiceMock.returnMyObservable.mockReturnValue( of( true ) );

        fixture.testFunction();

        expect( doAThingSpy ).toHaveBeenCalledWith( true );
    });
});

(这与 Jasmine 中的做法几乎相同)