test: exercise EE function type checking paths

This commit adds tests for on(), once(), removeListener(),
and prependOnceListener(), which all throw a TypeError if
the listener argument is not a function.

PR-URL: https://github.com/nodejs/node/pull/8168
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/test/parallel/test-event-emitter-once.js b/test/parallel/test-event-emitter-once.js
index 1da57ad45d..cca21a454b 100644
--- a/test/parallel/test-event-emitter-once.js
+++ b/test/parallel/test-event-emitter-once.js
@@ -1,8 +1,9 @@
 'use strict';
 const common = require('../common');
-var events = require('events');
+const assert = require('assert');
+const EventEmitter = require('events');
 
-var e = new events.EventEmitter();
+const e = new EventEmitter();
 
 e.once('hello', common.mustCall(function(a, b) {}));
 
@@ -26,3 +27,10 @@ e.once('e', common.mustCall(function() {
 e.once('e', common.mustCall(function() {}));
 
 e.emit('e');
+
+// Verify that the listener must be a function
+assert.throws(() => {
+  const ee = new EventEmitter();
+
+  ee.once('foo', null);
+}, /^TypeError: "listener" argument must be a function$/);