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

Exploratory testing is an informal test design technique that allows testers to dynamically control the test design during the testing process. This approach emphasizes the tester's creativity, skills, and intuition, enabling them to explore the application, learning about its functionalities and potential issues simultaneously. Since exploratory testing is not driven by predetermined test cases, testers can adapt their strategies based on their observations and findings in real-time. This flexibility allows for a more thorough and responsive testing process, as testers can follow up on interesting behaviors or unexpected results immediately.

The other options represent different types of testing but do not inherently support the dynamic control of test design. Regression testing involves running a predefined set of tests to ensure that new changes have not adversely affected existing functionality. Performance testing focuses on evaluating the system's responsiveness and stability under various conditions, typically following a set methodology. Static testing is a technique that involves reviewing and analyzing the code or documentation without executing the program, which does not lend itself to dynamic test design during an active testing phase.