要解决"Angular - karma 单元测试用例"的问题，你可以按照以下步骤进行操作：

1. 安装依赖：首先，确保你已经在项目中安装了Angular和Karma。如果没有，请在项目根目录下执行以下命令：

npm install @angular/cli --save-dev
npm install karma karma-chrome-launcher karma-jasmine karma-jasmine-html-reporter --save-dev

2. 创建测试用例：在项目的src文件夹下创建一个新的文件夹，用于存放测试用例文件。例如，创建一个名为"app"的文件夹，并在其中创建一个名为"app.component.spec.ts"的文件。

import { TestBed, async } from '@angular/core/testing';
import { AppComponent } from './app.component';

describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [
        AppComponent
      ],
    }).compileComponents();
  }));

  it('should create the app', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    expect(app).toBeTruthy();
  });

  it(`should have as title 'app'`, () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    expect(app.title).toEqual('app');
  });

  it('should render title', () => {
    const fixture = TestBed.createComponent(AppComponent);
    fixture.detectChanges();
    const compiled = fixture.debugElement.nativeElement;
    expect(compiled.querySelector('.content span').textContent).toContain('app app is running!');
  });
});

3. 配置Karma：在项目根目录下创建一个名为"karma.conf.js"的文件，并添加以下代码：

// karma.conf.js
module.exports = function(config) {
  config.set({
    basePath: '',
    frameworks: ['jasmine', '@angular/cli'],
    plugins: [
      require('karma-jasmine'),
      require('karma-chrome-launcher'),
      require('karma-jasmine-html-reporter'),
      require('@angular/cli/plugins/karma')
    ],
    client: {
      clearContext: false // leave Jasmine Spec Runner output visible in browser
    },
    coverageIstanbulReporter: {
      dir: require('path').join(__dirname, '../coverage'),
      reports: ['html', 'lcovonly'],
      fixWebpackSourcePaths: true
    },
    angularCli: {
      environment: 'dev'
    },
    reporters: ['progress', 'kjhtml'],
    port: 9876,
    colors: true,
    logLevel: config.LOG_INFO,
    autoWatch: true,
    browsers: ['Chrome'],
    singleRun: false
  });
};

4. 运行测试用例：在项目根目录下执行以下命令，来运行测试用例：

ng test

这样，你就可以运行Angular的Karma单元测试用例了。