要编写Angular 7的路由测试，可以按照以下步骤进行：

1. 创建路由文件：在src/app目录下创建一个名为app-routing.module.ts的文件，用于定义应用的路由。

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';

const routes: Routes = [
  { path: '', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

2. 创建组件文件：在src/app目录下创建两个组件文件home.component.ts和about.component.ts。

home.component.ts：

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

@Component({
  selector: 'app-home',
  template: '
Home Component
'
})
export class HomeComponent { }

about.component.ts：

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

@Component({
  selector: 'app-about',
  template: '
About Component
'
})
export class AboutComponent { }

3. 创建测试文件：在src/app目录下创建一个名为app-routing.module.spec.ts的文件，用于编写路由测试。

import { TestBed, async } from '@angular/core/testing';
import { RouterTestingModule } from '@angular/router/testing';
import { AppComponent } from './app.component';
import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';

describe('AppRoutingModule', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        RouterTestingModule.withRoutes([]),
      ],
      declarations: [
        AppComponent,
        HomeComponent,
        AboutComponent
      ],
    }).compileComponents();
  }));

  it('should navigate to home', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    const navigateSpy = spyOn(fixture.debugElement.injector.get(Router), 'navigate');

    app.goToHome();

    expect(navigateSpy).toHaveBeenCalledWith(['/']);
  });

  it('should navigate to about', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    const navigateSpy = spyOn(fixture.debugElement.injector.get(Router), 'navigate');

    app.goToAbout();

    expect(navigateSpy).toHaveBeenCalledWith(['/about']);
  });
});

4. 运行测试：在终端中运行ng test命令来执行测试。

以上代码示例是一个简单的路由测试，其中AppComponent是应用的根组件，goToHome和goToAbout是在根组件中定义的导航方法。在测试中，我们首先创建了一个测试模块，然后通过createComponent方法创建了根组件的实例，最后使用spyOn方法来监视路由导航方法的调用。通过expect断言来验证是否正确导航到了指定的路径。