如何导入共享模块（使用 Angular Material）来测试 Angular 应用程序？

我正在尝试为同样使用 Angular Material 和 Angular Flex 布局的 Angular 示例应用程序创建测试。

在我的应用程序中，我已经在使用共享模块来导入所有 Angular Material 组件。它是这样的：

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

import { MatButtonModule } from '@angular/material/button';
import { MatToolbarModule } from '@angular/material/toolbar';
import { MatIconModule } from '@angular/material/icon';
import { MatCardModule } from '@angular/material/card';
import { MatInputModule } from '@angular/material/input';
import { MatDatepickerModule } from '@angular/material/datepicker';
import { MatFormFieldModule } from '@angular/material/form-field';
import { MatNativeDateModule } from '@angular/material/core';
import { MatTabsModule } from '@angular/material/tabs';

@NgModule({
  imports: [
    MatButtonModule, MatToolbarModule, MatIconModule, MatCardModule,
    MatDatepickerModule, MatFormFieldModule, MatInputModule,
    MatTabsModule, MatNativeDateModule
  ],
  exports: [
    MatButtonModule, MatToolbarModule, MatIconModule, MatCardModule,
    MatDatepickerModule, MatFormFieldModule, MatInputModule,
    MatTabsModule
  ]
})
export class MaterialModule {}

当我第一次运行时，ng test每个组件都无法通过基本的创建测试。最肯定的是，消息提到了 Angular Material 标签。所以，我试过这个：

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { RouterTestingModule } from '@angular/router/testing';
import { AccountComponent } from './account.component';
import { MaterialModule } from '../material.module';

describe('AccountComponent', () => {
  let component: AccountComponent;
  let fixture: ComponentFixture<AccountComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [AccountComponent],
      imports: [
        RouterTestingModule,
        MaterialModule
      ]
    }).compileComponents();
  }));

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

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

然而，这个测试并没有通过。但是，我尝试手动导入模块，如错误消息所述：

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { RouterTestingModule } from '@angular/router/testing';
import { AccountComponent } from './account.component';
import { MatFormFieldModule } from '@angular/material/form-field';
import { MatTabsModule } from '@angular/material/tabs';
import { MatCardModule } from '@angular/material/card';

describe('AccountComponent', () => {
  let component: AccountComponent;
  let fixture: ComponentFixture<AccountComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [AccountComponent],
      imports: [
        RouterTestingModule,
        MatFormFieldModule,
        MatTabsModule,
        MatCardModule
      ]
    }).compileComponents();
  }));

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

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

令我惊讶的是，测试现在通过了。我真的想不通为什么。

无论如何，我可以在测试时像在常规应用程序中一样导入共享模块吗？