README.md

Check out this repository/download this ZIP. Run:

$ npm i --save-dev
$ npm test

> sinon-chrome-webext-test@0.0.1 test /.../sinon-chrome-webext-test
> karma start karma.conf.js

Firefox 57.0.0 (Ubuntu 0.0.0) ERROR
  ReferenceError: browser is not defined
  at test.js:1


npm ERR! Test failed.  See above for more details.

I expect this to run without error.

karma.conf.js

module.exports = function(config) {
  config.set({
    files: [
      './test.js',
    ],
    frameworks: ['sinon-chrome'],
    port: 7328,
    colors: true,
    logLevel: config.LOG_WARN,
    autoWatch: true,

    browsers: ['FirefoxHeadless'],
    // https://github.com/karma-runner/karma-firefox-launcher/issues/76
    customLaunchers: {
      FirefoxHeadless: {
        base: 'Firefox',
        flags: [ '-headless' ],
      },
    },

    singleRun: true,
    concurrency: Infinity
  })
}

package.json

{
  "name": "sinon-chrome-webext-test",
  "version": "0.0.1",
  "scripts": {
    "test": "karma start karma.conf.js"
  },
  "devDependencies": {
    "chai": "^4.1.2",
    "karma": "^1.3.0",
    "karma-firefox-launcher": "^1.0.0",
    "karma-chai": "^0.1.0",
    "karma-sinon-chrome": "git+https://github.com/arantius/karma-sinon-chrome.git#02ac98c75f795e62d9168d9cc8cefcc76b310116",
    "sinon-chrome": "^2.1.2"
  }
}

test.js

browser.runtime.getManifest.returns({'version': 1});