build(test): configure Karma browsers from env

karma.conf.js

@@ -1,6 +1,17 @@
 // Karma configuration file, see link for more information
 // https://karma-runner.github.io/1.0/config/configuration-file.html
 
+const DEFAULT_BROWSERS = ['Firefox'];
+
+function configuredBrowsers(envValue) {
+  if (!envValue) {
+    return DEFAULT_BROWSERS;
+  }
+
+  const browsers = envValue.split(',').map((browser) => browser.trim()).filter(Boolean);
+  return browsers.length ? browsers : DEFAULT_BROWSERS;
+}
+
 module.exports = function (config) {
   config.set({
     basePath: '',
@@ -27,7 +38,9 @@ module.exports = function (config) {
     colors: true,
     logLevel: config.LOG_INFO,
     autoWatch: true,
-    browsers: ['Firefox'],
+    browsers: configuredBrowsers(process.env.KARMA_BROWSERS),
     singleRun: false
   });
 };
+
+module.exports.configuredBrowsers = configuredBrowsers;

policy-tests/check-karma-browsers.js

@@ -0,0 +1,14 @@
+const assert = require('assert');
+const karmaConfig = require('../karma.conf.js');
+
+assert.deepStrictEqual(karmaConfig.configuredBrowsers(undefined), ['Firefox']);
+assert.deepStrictEqual(karmaConfig.configuredBrowsers(''), ['Firefox']);
+assert.deepStrictEqual(karmaConfig.configuredBrowsers('FirefoxHeadless'), ['FirefoxHeadless']);
+assert.deepStrictEqual(
+  karmaConfig.configuredBrowsers('ChromeHeadless, FirefoxHeadless'),
+  ['ChromeHeadless', 'FirefoxHeadless']
+);
+assert.deepStrictEqual(
+  karmaConfig.configuredBrowsers(' , FirefoxHeadless ,, '),
+  ['FirefoxHeadless']
+);

policy-tests/run-all.js

@@ -1,2 +1,3 @@
 require('./check-licenses.js');
 require('./check-commit-log.js');
+require('./check-karma-browsers.js');