feat: enable parallel mocha testing

.mocharc.js

@@ -0,0 +1,16 @@
+// Copyright IBM Corp. 2020. All Rights Reserved.
+// Node module: loopback-next
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+// Reuse the mocha config from `@loopback/cli`
+const config = require('./packages/cli/.mocharc.js');
+
+// Set max listeners to 16 for testing to avoid the following warning:
+// (node:11220) MaxListenersExceededWarning: Possible EventEmitter
+// memory leak detected. 11 SIGTERM listeners added to [process].
+// Use emitter.setMaxListeners() to increase limit
+// It only happens when multiple app instances are started but not stopped
+process.setMaxListeners(16);
+
+module.exports = config;

.vscode/launch.json

@@ -11,6 +11,7 @@
       "program": "${workspaceRoot}/packages/build/node_modules/mocha/bin/_mocha",
       "runtimeArgs": ["-r", "${workspaceRoot}/packages/build/node_modules/source-map-support/register"],
       "cwd": "${workspaceRoot}",
+      "autoAttachChildProcesses": true,
       "args": [
         "--config",
         "${workspaceRoot}/packages/build/config/.mocharc.json",
@@ -26,6 +27,7 @@
       "program": "${workspaceRoot}/bin/mocha-current-file",
       "runtimeArgs": ["-r", "${workspaceRoot}/packages/build/node_modules/source-map-support/register"],
       "cwd": "${workspaceRoot}",
+      "autoAttachChildProcesses": true,
       "args": [
         "--config",
         "${workspaceRoot}/packages/build/config/.mocharc.json",

packages/build/bin/run-mocha.js

@@ -15,6 +15,9 @@ Usage:
 
 'use strict';
 
+const path = require('path');
+const fs = require('fs-extra');
+
 function run(argv, options) {
   const utils = require('./utils');
 
@@ -24,7 +27,6 @@ function run(argv, options) {
     !utils.isOptionSet(
       mochaOpts,
       '--config', // mocha 6.x
-      '--opts', // legacy
       '--package', // mocha 6.x
       '--no-config', // mocha 6.x
     ) && !utils.mochaConfiguredForProject();
@@ -59,6 +61,17 @@ function run(argv, options) {
     mochaOpts.splice(lang, 2);
   }
 
+  // Set `--parallel` for `@loopback/*` packages
+  if (!mochaOpts.includes('--parallel')) {
+    const pkgFile = path.join(utils.getPackageDir(), 'package.json');
+    if (fs.existsSync(pkgFile)) {
+      const pkg = fs.readJsonSync(pkgFile);
+      if (pkg.name.startsWith('@loopback/')) {
+        mochaOpts.push('--parallel');
+      }
+    }
+  }
+
   const args = [...mochaOpts];
 
   return utils.runCLI('mocha/bin/mocha', args, options);

packages/build/bin/utils.js

@@ -228,7 +228,6 @@ function mochaConfiguredForProject() {
     '.mocharc.json',
     '.mocharc.yaml',
     '.mocharc.yml',
-    'test/mocha.opts',
   ];
   return configFiles.some(f => {
     const configFile = path.join(getPackageDir(), f);

packages/build/config/.mocharc.json

@@ -1,5 +1,5 @@
 {
-  "require": "source-map-support/register",
+  "require": ["source-map-support/register"],
   "recursive": true,
   "exit": true,
   "reporter": "dot"

packages/cli/.mocharc.js

@@ -0,0 +1,53 @@
+// Copyright IBM Corp. 2020. All Rights Reserved.
+// Node module: @loopback/cli
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+// A workaround to use `--require ./test/snapshot-matcher.js` so that root
+// hooks are executed by mocha parallel testing for each job
+
+const debug = require('debug')('loopback:cli:test');
+
+/**
+ * Build mocha config for `@loopback/cli`
+ */
+function buildConfig() {
+  // Use the default config from `@loopback/build`
+  const mochaConfig = require('@loopback/build/config/.mocharc.json');
+  debug('Default mocha config:', mochaConfig);
+  // Resolve `./test/snapshot-matcher.js` to get the absolute path
+  const mochaHooksFile = require.resolve('./test/snapshot-matcher.js');
+  debug('Root hooks for --require %s', mochaHooksFile);
+  const config = {...mochaConfig, timeout: 5000};
+
+  // Allow env var `MOCHA_JOBS` to override parallel testing parameters
+  const jobs = +process.env.MOCHA_JOBS;
+  if (jobs === 0) {
+    // Disable parallel testing
+    config.parallel = false;
+  } else if (jobs > 0) {
+    // Override the default number of concurrent jobs
+    config.parallel = true;
+    config.jobs = jobs;
+  }
+  addRequire(config, mochaHooksFile);
+  debug('Final mocha config:', config);
+  return config;
+}
+
+/**
+ * Add a new entry to the mocha config.require
+ * @param {object} config - Mocha config
+ * @param {string} mochaHooksFile - A module to be loaded by mocha
+ */
+function addRequire(config, mochaHooksFile) {
+  if (typeof config.require === 'string') {
+    config.require = [config.require, mochaHooksFile];
+  } else if (Array.isArray(config.require)) {
+    config.require = config.require.concat(mochaHooksFile);
+  } else {
+    config.require = mochaHooksFile;
+  }
+}
+
+module.exports = buildConfig();