test: improve coverage on removeListeners functions

PR-URL: #11140
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

Author: matsuda-koushi

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

@@ -82,3 +82,9 @@ function listener() {}
   const ee = new events.EventEmitter();
   assert.deepStrictEqual(ee, ee.removeAllListeners());
 }
+
+{
+  const ee = new events.EventEmitter();
+  ee._events = undefined;
+  assert.strictEqual(ee, ee.removeAllListeners());
+}

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

@@ -128,3 +128,11 @@ assert.throws(() => {
 
   ee.removeListener('foo', null);
 }, /^TypeError: "listener" argument must be a function$/);
+
+{
+  const ee = new EventEmitter();
+  const listener = () => {};
+  ee._events = undefined;
+  const e = ee.removeListener('foo', listener);
+  assert.strictEqual(e, ee);
+}