A company asks a vendor to help its internal red team with a penetration test...

This scenario describes a partially-known environment penetration test. In CompTIA Security+ SY0-701, penetration testing approaches are commonly categorized as black box (unknown), white box (fully known), and gray box (partially known). A partially-known environment means the tester is given limited information—enough to be realistic and efficient, but not complete details about the infrastructure.

Here, the vendor is assisting an internal red team and is intentionally not provided with extensive infrastructure details, which mirrors a gray-box testing approach. This method balances realism and efficiency by simulating an attacker who has some knowledge (such as credentials, architecture diagrams, or application details) but not full access or documentation.

Passive reconnaissance (A) is an activity within testing, not a testing methodology. Integrated testing (C) refers to coordinated testing involving multiple teams (e.g., red and blue teams) with full cooperation. Defensive testing (D) focuses on validating defensive controls rather than simulating an attacker’s perspective.

Therefore, the correct answer is B: Partially-known environment.