Which of the following is an example of penetration testing?

Implementing a Host Intrusion Detection System (HIDS) is a passive, defensive monitoring control that detects suspicious activity - it does not simulate an attack.

Penetration testing is defined as simulating a real-world attack against a target network in a controlled, authorized manner to identify weaknesses before malicious actors can exploit them. Unlike detection or prevention tools, it actively probes the environment using attacker techniques and methodologies.

Implementing a Network Intrusion Detection System (NIDS) is a reactive detection mechanism that monitors traffic for known attack signatures, not an offensive testing activity.

Configuring a firewall to block unauthorized traffic is a preventive security control, which is the opposite of the offensive simulation that defines penetration testing.