Tests: Assure that UE does not regress via ue ls

Author: https://github.com/Hendiadyoin1
Commit: https://github.com/SerenityOS/serenity/commit/bdde44a8330
Pull-request: https://github.com/SerenityOS/serenity/pull/8703
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/alimpfard ✅
Reviewed-by: https://github.com/sin-ack

Tests/UserspaceEmulator/test-run-ls.cpp

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2021, Leon Albrecht <leon2002.la@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <stdlib.h>
+
+int main() { return system("UserspaceEmulator ls"); }