Bugfix is one of the classic types of tasks on CodeSignal. This type of task involves finding and correcting a single mistake within an otherwise correct block of pre-written code. This allows the candidate to provide a signal of their understanding in a shorter period of time, since they don’t have to write all of the code themselves.
This kind of task can also be used to assess a candidate’s code review skills, which can be another important part of the real-world dev experience. Even if the candidate would be able to solve the task by rewriting their own algorithm, bugfix tasks allow them to change only one line, so they have no choice but to engage with the reasoning of the dev who originally wrote the code.
As an additional anti-cheat measure, there’s a limit to how many characters the candidate can modify, based on the size of the expected solution (with some padding). Furthermore, these checks are administered on the client end, so the code won’t even be sent to the coderunner server if too much of the original code has been modified.