Which of the following is considered the odd one out among testing techniques?

The choice identified as the odd one out is indeed correct because it pertains to a different category of testing techniques compared to the others. White box, glass box, and structural testing techniques are all types of white-box testing methods that focus on the internal structures, algorithms, and workings of the software. These approaches require knowledge of the programming code and involve testing individual statements, paths, and conditions within the codebase.

In contrast, functional testing is focused on the software's functional requirements and specifications. It assesses what the software does rather than how the features are implemented internally. Functional testing techniques verify that the software behaves as expected from the user's perspective and are typically concerned with inputs, outputs, and the user interface, irrespective of the underlying code structure.

This distinction is fundamental; the first three options are techniques relevant to white-box testing, which is concerned with internal logic, while functional testing is centered on user-facing functionalities, making it the odd one out among the listed options.