Schematics for Component spec should use test host component when created with `-cd OnPush`

執行 ng generate component test -cd OnPush 並檢查產生的元件檔案和 .spec 檔案，重點關注 Angular component schematic 如何設定測試。以連結的 Angular 測試指南作為脈絡，接著確認產生的測試使用測試主機元件模式，且重複呼叫 fixture.detectChanges() 會觸發變更偵測。

Versions

Angular CLI: 1.7.3
Node: 8.9.1
OS: win32 x64
Angular: 5.2.1
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, platform-server, router

@angular/cli: 1.7.3
@angular-devkit/build-optimizer: 0.3.2
@angular-devkit/core: 0.3.2
@angular-devkit/schematics: 0.3.2
@ngtools/json-schema: 1.2.0
@ngtools/webpack: 1.10.2
@schematics/angular: 0.3.2
@schematics/package-update: 0.3.2
typescript: 2.4.2
webpack: 3.11.0

Repro steps

• ng generate component test -cd OnPush
• Edit the test.component.html to be

{{ checkMe() }}

• Add the checkMe method to test.component.ts:

checkMe() {
      console.log('change detection was invoked!');
}

• Edit the generated .spec file to include the following test:

fit('runs change detection', () => {
    fixture.detectChanges();
    fixture.detectChanges();
    fixture.detectChanges();
});

• Run unit test

Observed behavior

'change detection was invoked!' is logged only once (the initial check on creation of the component) rather than 4 times. That is to say, invoking fixture.detectChanges() does not actually run change detection. This is a known issue and is discussed in https://github.com/angular/angular/issues/12313

LOG: 'change detection was invoked!'
Chrome 65.0.3325 (Windows 10 0.0.0): Executed 1 of 478 SUCCESS (0 secs / 0.138 secs)

Desired behavior

As discussed in the thread linked above, the solution for testing OnPush components is to use the "test host component" pattern as described in the angular.io testing docs.

Therefore, the Angular CLI should use a schematic which uses the test host component when the -cd OnPush flag has been used. Otherwise we get a default test setup which is not fit for purpose (and will cause many wasted hours for devs like me 😓)