test: exercise once() with varying arguments

This commit regains test coverage for EventEmitter#once() with
four or more arguments. To avoid similar regressions in the
future, once() is called with enough arguments to cover all of
the separate code paths.

PR-URL: https://github.com/nodejs/node/pull/13524
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-event-emitter-once.js

@@ -55,3 +55,23 @@ assert.throws(() => {
 
   ee.once('foo', null);
 }, /^TypeError: "listener" argument must be a function$/);
+
+{
+  // once() has different code paths based on the number of arguments being
+  // emitted. Verify that all of the cases are covered.
+  const maxArgs = 4;
+
+  for (let i = 0; i <= maxArgs; ++i) {
+    const ee = new EventEmitter();
+    const args = ['foo'];
+
+    for (let j = 0; j < i; ++j)
+      args.push(j);
+
+    ee.once('foo', common.mustCall((...params) => {
+      assert.deepStrictEqual(params, args.slice(1));
+    }));
+
+    EventEmitter.prototype.emit.apply(ee, args);
+  }
+}