Vulnerability testing where you have knowledge of the systems involved is called?

Vulnerability testing that involves knowledge of the systems is referred to as Static Application Security Testing (SAST). This approach allows testers to examine the internal workings of an application, including its source code, configuration files, and other elements, to identify potential vulnerabilities. SAST is typically conducted early in the software development life cycle, enabling developers to address security issues before deployment.

In contrast, other testing methods like Dynamic Application Security Testing (DAST) do not require knowledge of the internal workings and instead focus on analyzing the application in its runtime environment, often leading to different types of insights. While hybrid approaches may incorporate both static and dynamic testing methods, SAST is specifically characterized by its focus on code and architecture with insider knowledge of the application. Penetration testing, or "pen" testing, is another methodology but is often performed under the assumption of an external perspective, simulating an attacker's approach. Thus, SAST is the most accurate descriptor of vulnerability testing involving awareness of system details.