test: improve code in test-domain-multi

* use common.mustCall to validate functions executions
* use common.fail to control error
* remove unnecessary variables
* remove unnecessary assertions
* remove console.log and console.error
* use arrow functions

PR-URL: nodejs#10798
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-domain-multi.js

@@ -1,26 +1,16 @@
 'use strict';
 // Tests of multiple domains happening at once.
 
-require('../common');
-const assert = require('assert');
+const common = require('../common');
 const domain = require('domain');
-
-let caughtA = false;
-let caughtB = false;
-let caughtC = false;
-
+const http = require('http');
 
 const a = domain.create();
 a.enter(); // this will be our "root" domain
-a.on('error', function(er) {
-  caughtA = true;
-  console.log('This should not happen');
-  throw er;
-});
 
+a.on('error', common.fail);
 
-const http = require('http');
-const server = http.createServer(function(req, res) {
+const server = http.createServer((req, res) => {
   // child domain of a.
   const b = domain.create();
   a.add(b);
@@ -31,47 +21,34 @@ const server = http.createServer(function(req, res) {
   b.add(req);
   b.add(res);
 
-  b.on('error', function(er) {
-    caughtB = true;
-    console.error('Error encountered', er);
+  b.on('error', common.mustCall((er) => {
     if (res) {
       res.writeHead(500);
       res.end('An error occurred');
     }
     // res.writeHead(500), res.destroy, etc.
     server.close();
-  });
+  }));
 
   // XXX this bind should not be necessary.
   // the write cb behavior in http/net should use an
   // event so that it picks up the domain handling.
-  res.write('HELLO\n', b.bind(function() {
+  res.write('HELLO\n', b.bind(() => {
     throw new Error('this kills domain B, not A');
   }));
 
-}).listen(0, function() {
+}).listen(0, () => {
   const c = domain.create();
-  const req = http.get({ host: 'localhost', port: this.address().port });
+  const req = http.get({ host: 'localhost', port: server.address().port });
 
   // add the request to the C domain
   c.add(req);
 
-  req.on('response', function(res) {
-    console.error('got response');
+  req.on('response', (res) => {
     // add the response object to the C domain
     c.add(res);
     res.pipe(process.stdout);
   });
 
-  c.on('error', function(er) {
-    caughtC = true;
-    console.error('Error on c', er.message);
-  });
-});
-
-process.on('exit', function() {
-  assert.strictEqual(caughtA, false);
-  assert.strictEqual(caughtB, true);
-  assert.strictEqual(caughtC, true);
-  console.log('ok - Errors went where they were supposed to go');
+  c.on('error', common.mustCall((er) => { }));
 });