karma.conf.js

const { createDefaultConfig } = require('@open-wc/testing-karma');
const merge = require('deepmerge');

module.exports = config => {
  config.set(
    merge(createDefaultConfig(config), {
      files: [
        // runs all files ending with .test in the test folder,
        // can be overwritten by passing a --grep flag. examples:
        //
        // npm run test -- --grep test/foo/bar.test.js
        // npm run test -- --grep test/bar/*
        { pattern: config.grep ? config.grep : 'tests/**/*.test.js', type: 'module' }
      ],
      browserConsoleLogOptions: { level: 'error' },
      coverageIstanbulReporter: {
        dir:'dist/coverage'
      },
      // see the karma-esm docs for all options
      esm: {
        // if you are using 'bare module imports' you will need this option
        nodeResolve: true
      }
    })
  );
  return config;
};