A CUnit developer specializes in using the CUnit framework, a lightweight system for unit testing software written in the C language. They write small, isolated tests for individual components of the software to ensure each part functions correctly. These developers play a crucial role in improving software quality, detecting issues early, and facilitating changes by ensuring existing functionalities are not broken. They also help in maintaining documentation of tests and results, assisting in debugging, and making the software development process more agile and efficient. The CUnit developer's work is pivotal in preventing errors and enhancing software reliability.