Which informal test design technique allows the tester to control test design dynamically while testing?

The correct choice focuses on exploratory testing, which is an informal test design technique that emphasizes tester autonomy and adaptability during the testing process. In exploratory testing, testers actively engage with the application without strict pre-defined test cases. They use their insights, experience, and creativity to design and execute tests dynamically based on the behavior of the application as they explore it.

This technique allows testers to adjust their approach in real-time, responding to unexpected issues or areas of interest that arise during testing. This flexibility is especially beneficial in agile environments, where rapid iteration and immediate feedback are crucial.

In contrast, regression testing, performance testing, and static testing rely more on previously defined criteria, models, or specifications. Regression testing typically involves running a set of predefined test cases to ensure that existing functionality still works after changes are made. Performance testing assesses application behavior under load, often based on standard metrics and criteria set prior to testing, while static testing focuses on reviewing specifications and code without execution and does not allow for dynamic control in the same way. Thus, exploratory testing stands out as the approach that facilitates real-time test design based on ongoing observations.