What type of testing evaluates code in a runtime environment without requiring access to source code?

Dynamic testing evaluates code while it is executing, allowing testers to observe the behavior of the application in its runtime environment. This type of testing is crucial for identifying issues that may not be evident when analyzing the source code alone. By executing the program, dynamic testing helps to uncover runtime errors, memory leaks, and performance issues, which can occur due to environment-related factors or integration with other components.

In contrast, static testing refers to examining the code without running it, focusing on reviewing source code or documentation to identify potential flaws. Whitebox testing involves having access to the internal structures or workings of an application, including the source code, which is not a requirement in dynamic testing. Regression testing, on the other hand, is performed to ensure that recent changes in the codebase haven't adversely affected existing features, and can be considered part of dynamic testing. However, it specifically focuses on verifying that previously developed and tested software continues to perform after a change.

Thus, dynamic testing is the technique that specifically operates in the runtime environment without needing the source code, making it the correct answer.