test: refactor test-cluster-setup-master

- use mustCall instead of counters
- include totalWorkers and settings in the error messages

PR-URL: nodejs/node#16065
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>

Author: Jean-Baptiste Brossard

test/parallel/test-cluster-setup-master.js

@@ -20,7 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const cluster = require('cluster');
 
@@ -38,7 +38,7 @@ if (cluster.isWorker) {
   };
 
   const totalWorkers = 2;
-  let onlineWorkers = 0;
+  let settings;
 
   // Setup master
   cluster.setupMaster({
@@ -49,7 +49,7 @@ if (cluster.isWorker) {
   cluster.once('setup', function() {
     checks.setupEvent = true;
 
-    const settings = cluster.settings;
+    settings = cluster.settings;
     if (settings &&
         settings.args && settings.args[0] === 'custom argument' &&
         settings.silent === true &&
@@ -58,37 +58,36 @@ if (cluster.isWorker) {
     }
   });
 
-  let correctIn = 0;
+  let correctInput = 0;
 
-  cluster.on('online', function lisenter(worker) {
-
-    onlineWorkers++;
+  cluster.on('online', common.mustCall(function listener(worker) {
 
     worker.once('message', function(data) {
-      correctIn += (data === 'custom argument' ? 1 : 0);
-      if (correctIn === totalWorkers) {
+      correctInput += (data === 'custom argument' ? 1 : 0);
+      if (correctInput === totalWorkers) {
         checks.args = true;
       }
       worker.kill();
     });
 
-    // All workers are online
-    if (onlineWorkers === totalWorkers) {
-      checks.workers = true;
-    }
-  });
+  }, totalWorkers));
 
   // Start all workers
   cluster.fork();
   cluster.fork();
 
   // Check all values
   process.once('exit', function() {
-    assert.ok(checks.workers, 'Not all workers went online');
-    assert.ok(checks.args, 'The arguments was noy send to the worker');
+    const argsMsg = 'Arguments was not send for one or more worker. ' +
+                    `${correctInput} workers receive argument, ` +
+                    `but ${totalWorkers} were expected.`;
+    assert.ok(checks.args, argsMsg);
+
     assert.ok(checks.setupEvent, 'The setup event was never emitted');
-    const m = 'The settingsObject do not have correct properties';
-    assert.ok(checks.settingsObject, m);
+
+    const settingObjectMsg = 'The settingsObject do not have correct ' +
+                             `properties : ${JSON.stringify(settings)}`;
+    assert.ok(checks.settingsObject, settingObjectMsg);
   });
 
 }