Added option browser launching for the test command

The purpose of this PR is to be able to easily run karma tests in other
browsers without manually editing the karma configuration or making
local copies of the karma configuration.

Additions:

- `yarn test --no-browser` to avoid launching the default browser.
  It is up to the developer to run the tests in whatever browser she/he
  chooses by navigating to http://localhost:9876/.

- `yarn test --browser <browser>` run the tests in a different
  browser/s instead of the default browser. Chrome launcher comes by
  default with karma. Firefox, Safari and others can be installed
  independently.

Modifications:

- `yarn gulp test-watch` has been substituted by `yarn test --watch` for consistency.

Makefile

@@ -23,18 +23,18 @@ dev: node_modules/.uptodate
 
 .PHONY: test
 test: node_modules/.uptodate
-ifdef FILTER
-	yarn test --grep $(FILTER)
+ifdef ARGS
+	yarn test $(ARGS)
 else
 	yarn test
 endif
 
 .PHONY: servetests
 servetests: node_modules/.uptodate
-ifdef FILTER
-	node_modules/.bin/gulp test-watch --grep $(FILTER)
+ifdef ARGS
+	node_modules/.bin/gulp --watch $(ARGS)
 else
-	node_modules/.bin/gulp test-watch
+	node_modules/.bin/gulp --watch
 endif
 
 .PHONY: lint

gulpfile.js

@@ -34,17 +34,34 @@ const IMAGES_DIR = 'build/images';
 function parseCommandLine() {
   commander
     .option(
-      '--grep [pattern]',
-      'Run only tests where filename matches a pattern'
+      '--grep <pattern>',
+      'Run only tests where filename matches a regex pattern'
+    )
+    .option('--watch', 'Continuously run tests (default: false)', false)
+    .option('--browser <browser>', 'Run tests in browser of choice.')
+    .option(
+      '--no-browser',
+      "Don't launch default browser. Instead, navigate to http://localhost:9876/ to run the tests."
     )
     .parse(process.argv);
 
-  return {
-    grep: commander.opts().grep,
+  const { grep, watch, browser } = commander.opts();
+  const karmaOptions = {
+    grep: grep,
+    singleRun: !watch,
   };
+
+  // browser option can be either false | undefined | string
+  if (browser === false) {
+    karmaOptions.browsers = null;
+  } else if (browser) {
+    karmaOptions.browsers = [browser];
+  }
+
+  return karmaOptions;
 }
 
-const taskArgs = parseCommandLine();
+const karmaOptions = parseCommandLine();
 
 /** A list of all modules included in vendor bundles. */
 const vendorModules = Object.keys(vendorBundles.bundles).reduce(function (
@@ -361,13 +378,12 @@ gulp.task(
   )
 );
 
-function runKarma({ singleRun }, done) {
+function runKarma(done) {
   const karma = require('karma');
   new karma.Server(
     {
       configFile: path.resolve(__dirname, './src/karma.config.js'),
-      grep: taskArgs.grep,
-      singleRun,
+      ...karmaOptions,
     },
     done
   ).start();
@@ -377,9 +393,5 @@ function runKarma({ singleRun }, done) {
 // Some (eg. a11y) tests rely on CSS bundles, so build these first.
 gulp.task(
   'test',
-  gulp.series('build-css', done => runKarma({ singleRun: true }, done))
-);
-gulp.task(
-  'test-watch',
-  gulp.series('build-css', done => runKarma({ singleRun: false }, done))
+  gulp.series('build-css', done => runKarma(done))
 );