test: expand test coverage of events.js

* test else path in emitMany function
* test calling removeAllListeners() in a event emitter instance
  with no events at all
* test calling removeListener() passing a event type that does
  not exist
* test calling eventNames() in a event emitter instance
  with no events at all

Refs: https://coverage.nodejs.org/coverage-ba776b3a56642d4c/root/events.js.html
PR-URL: #10947
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/parallel/test-event-emitter-num-args.js

@@ -4,15 +4,20 @@ var assert = require('assert');
 var events = require('events');
 
 const e = new events.EventEmitter();
-const num_args_emited = [];
+const num_args_emitted = [];
 
 e.on('numArgs', function() {
-  var numArgs = arguments.length;
-  console.log('numArgs: ' + numArgs);
-  num_args_emited.push(numArgs);
+  const numArgs = arguments.length;
+  num_args_emitted.push(numArgs);
 });
 
-console.log('start');
+e.on('foo', function() {
+  num_args_emitted.push(arguments.length);
+});
+
+e.on('foo', function() {
+  num_args_emitted.push(arguments.length);
+});
 
 e.emit('numArgs');
 e.emit('numArgs', null);
@@ -21,6 +26,8 @@ e.emit('numArgs', null, null, null);
 e.emit('numArgs', null, null, null, null);
 e.emit('numArgs', null, null, null, null, null);
 
+e.emit('foo', null, null, null, null);
+
 process.on('exit', function() {
-  assert.deepStrictEqual([0, 1, 2, 3, 4, 5], num_args_emited);
+  assert.deepStrictEqual([0, 1, 2, 3, 4, 5, 4, 4], num_args_emitted);
 });

test/parallel/test-event-emitter-remove-listeners.js

@@ -116,6 +116,12 @@ function listener2() {}
   ee.emit('hello');
 }
 
+{
+  const ee = new EventEmitter();
+
+  assert.deepStrictEqual(ee, ee.removeListener('foo', () => {}));
+}
+
 // Verify that the removed listener must be a function
 assert.throws(() => {
   const ee = new EventEmitter();

test/parallel/test-event-emitter-special-event-names.js

@@ -7,6 +7,8 @@ const assert = require('assert');
 const ee = new EventEmitter();
 const handler = () => {};
 
+assert.deepStrictEqual(ee.eventNames(), []);
+
 assert.strictEqual(ee._events.hasOwnProperty, undefined);
 assert.strictEqual(ee._events.toString, undefined);