events,test: fix TypeError in EventEmitter warning

Allows Symbol to be converted to String so it can be included in the
error.

Fixes: https://github.com/nodejs/node/issues/9003
PR-URL: https://github.com/nodejs/node/pull/9021
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js b/test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js
new file mode 100644
index 0000000000..fc0a3dba0e
--- /dev/null
+++ b/test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js
@@ -0,0 +1,24 @@
+// Flags: --no-warnings
+// The flag suppresses stderr output but the warning event will still emit
+'use strict';
+
+const common = require('../common');
+const events = require('events');
+const assert = require('assert');
+
+const symbol = Symbol('symbol');
+
+const e = new events.EventEmitter();
+e.setMaxListeners(1);
+
+process.on('warning', common.mustCall((warning) => {
+  assert.ok(warning instanceof Error);
+  assert.strictEqual(warning.name, 'MaxListenersExceededWarning');
+  assert.strictEqual(warning.emitter, e);
+  assert.strictEqual(warning.count, 2);
+  assert.strictEqual(warning.type, symbol);
+  assert.ok(warning.message.includes('2 Symbol(symbol) listeners added.'));
+}));
+
+e.on(symbol, function() {});
+e.on(symbol, function() {});