Angular6+单元测试中的spyOnisDevMode（）？

我的代码包含if这样的代码块

服务：

import { isDevMode } from '@angular/core';

export class MyService {
  constructor() {}

  methodToTest(): {
    if (!isDevMode()) {
      doSomething();
    } else {
      doSomethingDifferentInDevMode();
    }
  }
}

my-service.spec.ts（仅相关行）：

it('should run doSomething() when isDevMode() returns false', () => {
  // what should i do here to mock a false value return for isDevMode() ?
  expect(doSomething).toHaveBeenCalled();
});

我如何监视isDevMode()此单个Angular单元测试使其返回false，以便我可以测试doSomething()被调用的？

首先将此函数包装到服务中：

import { isDevMode, Injectable } from '@angular/core';

@Injectable({ providedIn: 'root' })
export class DevModeService {
  constructor() {}

  isDevMode() {
    return isDevMode();
  }
}

然后，可以像使用任何其他服务一样在任何地方注入此服务：

import { DevModeService } from 'dev-mode.service';

export class MyService {
  constructor(private devModeService: DevModeService) {}

  methodToTest(): {
    if (!this.devModeService.isDevMode()) {
      doSomething();
    } else {
      doSomethingElse();
    }
  }
}

然后，您可以在测试MyService时监视DevModeService，就像对其他任何依赖项一样：

it('should do something when in dev mode') {
  const devModeService: DevModeService = TestBed.get(DevModeService);
  spyOn(devModeService, 'isDevMode').and.returnValue(true);

  const myService: MyService = TestBed.get(MyService);
  myService.methodToTest();
  // ...
}

it('should do something else when in prod mode') {
  const devModeService: DevModeService = TestBed.get(DevModeService);
  spyOn(devModeService, 'isDevMode').and.returnValue(false);

  const myService: MyService = TestBed.get(MyService);
  myService.methodToTest();
  // ...
}