为什么因果报导不起作用

Question

我的项目是Vue项目。

karma.conf：

let webpackConfig = require('../../build/webpack.test.conf');

module.exports = function karmaConfig (config) {
  config.set({
    // to run in additional browsers:
    // 1. install corresponding karma launcher
    //    http://karma-runner.github.io/0.13/config/browsers.html
    // 2. add it to the `browsers` array below.
    // browsers: ['PhantomJS'],
    browsers: ['Chrome'],
    frameworks: ['mocha', 'sinon-chai'],
    reporters: ['spec', 'coverage'],
    files: [
      './index.js'
    ],
    autoWatch: true,
    preprocessors: {
      './index.js': ['webpack', 'sourcemap']
    },
    webpack: webpackConfig,
    webpackMiddleware: {
      noInfo: true
    },
    coverageReporter: {
      dir: './coverage',
      reporters: [
        { type: 'lcov', subdir: '.' },
        { type: 'text-summary' }
      ]
    }
  })
};

输出：

由于我编写了13个测试用例，因此覆盖范围似乎无效。我想找出原因，请帮助我。