在Angular 2中测试ngOnChanges生命周期挂钩

Question

给定以下代码，我尝试测试Angular2的ngOnChanges生命周期钩子：

import {
    it,
    inject,
    fdescribe,
    beforeEachProviders,
} from '@angular/core/testing';

import {TestComponentBuilder} from '@angular/compiler/testing';

import {Component, OnChanges, Input} from '@angular/core';

@Component({
    selector: 'test',
    template: `<p>{{value}}</p>`,
})
export class TestComponent implements OnChanges {
    @Input() value: string;

    ngOnChanges(changes: {}): any {
        // should be called
    }
}

fdescribe('TestComponent', () => {
    let tcb: TestComponentBuilder;

    beforeEachProviders(() => [
        TestComponentBuilder,
        TestComponent,
    ]);

    beforeEach(inject([TestComponentBuilder], _tcb => {
        tcb = _tcb;
    }));

    it('should call ngOnChanges', done => {
        tcb.createAsync(TestComponent).then(fixture => {
            let testComponent: TestComponent = fixture.componentInstance;

            spyOn(testComponent, 'ngOnChanges').and.callThrough();

            testComponent.value = 'Test';
            fixture.detectChanges();

            expect(testComponent.ngOnChanges).toHaveBeenCalled();
            done();
        }).catch(e => done.fail(e));
    });
});

不幸的是，测试失败了，出现消息Expected spy ngOnChanges to have been called.我知道在这个例子中我只能检查HTML元素的内容，但是我有一些代码需要在ngOnChanes生命周期钩子中测试，所以这对我来说不是一个解决方案。我也不想在测试中直接调用testComponent.ngOnChanges({someMockData});。

如何从测试中设置TestComponent.value，以便调用ngOnChanges？

Answer 1

我想我来派对有点晚了，不过这对将来的一些人可能会有用。

自从angular的RC5发布以来，测试有了一些变化。然而，这里的主要问题是，当以编程方式设置输入时，不会调用ngOnChanges。See this for more info。基本上，当输入通过仅供查看的传递时，OnChanges挂钩被触发为。

这个问题的解决方案是让主机组件成为测试组件的父组件，并通过主机组件的模板传递输入。

以下是完整的工作代码：

import {Component, OnChanges, Input, ViewChild} from '@angular/core';
import { TestBed }      from '@angular/core/testing';

@Component({
    selector: 'test',
    template: `<p>{{value}}</p>`,
})
export class TestComponent implements OnChanges {
    @Input() value: string;

    ngOnChanges(changes: {}): any {
        // should be called
    }
}
/* In the host component's template we will pass the inputs to the actual
 * component to test, that is TestComponent in this case
 */
@Component({
    selector : `test-host-component`,
    template :
    `<div><test [value]="valueFromHost"></test></div>`
})
export class TestHostComponent {
    @ViewChild(TestComponent) /* using viewChild we get access to the TestComponent which is a child of TestHostComponent */
    public testComponent: any;
    public valueFromHost: string; /* this is the variable which is passed as input to the TestComponent */
}

describe('TestComponent', () => {

    beforeEach(() => {
        TestBed.configureTestingModule({declarations: [TestComponent,TestHostComponent]}); /* We declare both the components as part of the testing module */
    });

    it('should call ngOnChanges', ()=> {
        const fixture = TestBed.createComponent(TestHostComponent);
        const hostComponent = fixture.componentInstance;
        hostComponent.valueFromHost = 'Test';
        const component = hostComponent.testComponent;
        spyOn(component, 'ngOnChanges').and.callThrough();
        fixture.detectChanges();
        expect(component.ngOnChanges).toHaveBeenCalled();
    })


});

Answer 2

您还可以选择手动调用ngOnChanges钩子，并将所需的更改对象传递到那里。但这并不设置组件属性，只调用更改逻辑。

const previousValue = moment('2016-03-01T01:00:00Z');
const currentValue = moment('2016-02-28T01:00:00Z');

const changesObj: SimpleChanges = {
  prop1: new SimpleChange(previousValue, currentValue),
};

component.ngOnChanges(changesObj);

请注意，这种方法可以很好地测试ngOnChanges内部的逻辑，但它不会测试@Input装饰器是否设置正确。

Answer 3

在Angular 4中，要在测试时手动触发ngOnChanges()，您必须手动进行调用(如上所述)，只需要匹配new call signature of SimpleChange()

let prev_value = 'old';
let new_value = 'new';
let is_first_change: boolean = false;

component.ngOnChanges({
  prop1: new SimpleChange(prev_value, new_value, is_first_change),
});