Add watch option to test script

scripts/frontend/test.js

@@ -5,19 +5,24 @@ const { EOL } = require('os');
 const program = require('commander');
 const chalk = require('chalk');
 
+const SUCCESS_CODE = 0;
 const JEST_ROUTE = 'spec/frontend';
 const KARMA_ROUTE = 'spec/javascripts';
 const COMMON_ARGS = ['--colors'];
-const JEST_ARGS = ['--passWithNoTests'];
-const KARMA_ARGS = ['--no-fail-on-empty-test-suite'];
-const SUCCESS_CODE = 0;
+const jestArgs = [...COMMON_ARGS, '--passWithNoTests'];
+const karmaArgs = [...COMMON_ARGS, '--no-fail-on-empty-test-suite'];
 
 program
-  .version('0.1.0')
   .usage('[options] <file ...>')
   .option('-p, --parallel', 'Run tests suites in parallel')
+  .option(
+    '-w, --watch',
+    'Rerun tests when files change (tests will be run in parallel if this enabled)',
+  )
   .parse(process.argv);
 
+const shouldParallelize = program.parallel || program.watch;
+
 const isSuccess = code => code === SUCCESS_CODE;
 
 const combineExitCodes = codes => {
@@ -31,7 +36,7 @@ const skipIfFail = fn => code => (isSuccess(code) ? fn() : code);
 const endWithEOL = str => (str[str.length - 1] === '\n' ? str : `${str}${EOL}`);
 
 const runTests = paths => {
-  if (program.parallel) {
+  if (shouldParallelize) {
     return Promise.all([runJest(paths), runKarma(paths)]).then(combineExitCodes);
   } else {
     return runJest(paths).then(skipIfFail(() => runKarma(paths)));
@@ -73,11 +78,11 @@ const spawnYarnScript = (cmd, args) => {
 };
 
 const runJest = args => {
-  return spawnYarnScript('jest', [...JEST_ARGS, ...COMMON_ARGS, ...toJestArgs(args)]);
+  return spawnYarnScript('jest', [...jestArgs, ...toJestArgs(args)]);
 };
 
 const runKarma = args => {
-  return spawnYarnScript('karma', [...KARMA_ARGS, ...COMMON_ARGS, ...toKarmaArgs(args)]);
+  return spawnYarnScript('karma', [...karmaArgs, ...toKarmaArgs(args)]);
 };
 
 const replacePath = to => path =>
@@ -96,6 +101,10 @@ const toKarmaArgs = paths =>
   paths.reduce((acc, path) => acc.concat('-f', replacePathForKarma(path)), []);
 
 const main = paths => {
+  if (program.watch) {
+    jestArgs.push('--watch');
+    karmaArgs.push('--single-run', 'false', '--auto-watch');
+  }
   runTests(paths).then(code => {
     console.log('~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~');
     if (isSuccess(code)) {