Which of the following is NOT a common software testing methodology learned by trainees?

The correct answer is based on the distinction between the term "application testing" and the other three widely recognized software testing methodologies. Unit testing, integration testing, and system testing are foundational practices in software development.

Unit testing focuses on verifying individual components or functions of the code to ensure they work as intended. Integration testing follows by assessing how different components interact with each other after being integrated, identifying issues that can arise from their interactions. System testing evaluates the complete and integrated software application in its entirety, ensuring that it meets specified requirements and functions correctly as a whole.

On the other hand, "application testing" is not a specific methodology recognized in the same way as the others. While it might refer to testing an application in a general sense, it lacks the defined processes and structured approach that characterizes unit, integration, and system testing. Therefore, "application testing" does not align with the common methodologies that trainees typically learn.