test: add common.noop, default for common.mustCall()

Export a new common.noop no-operation function for general use.
Allow using common.mustCall() without a fn argument to simplify
test cases.

Replace various non-op functions throughout tests with common.noop

PR-URL: https://github.com/nodejs/node/pull/12027
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/test/parallel/test-event-emitter-listener-count.js b/test/parallel/test-event-emitter-listener-count.js
index ebfed8b2ee..50247f4277 100644
--- a/test/parallel/test-event-emitter-listener-count.js
+++ b/test/parallel/test-event-emitter-listener-count.js
@@ -1,15 +1,15 @@
 'use strict';
 
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const EventEmitter = require('events');
 
 const emitter = new EventEmitter();
-emitter.on('foo', function() {});
-emitter.on('foo', function() {});
-emitter.on('baz', function() {});
+emitter.on('foo', common.noop);
+emitter.on('foo', common.noop);
+emitter.on('baz', common.noop);
 // Allow any type
-emitter.on(123, function() {});
+emitter.on(123, common.noop);
 
 assert.strictEqual(EventEmitter.listenerCount(emitter, 'foo'), 2);
 assert.strictEqual(emitter.listenerCount('foo'), 2);