Unit testing in Go can be categorized into two main types: black box testing and white box testing. Black box testing focuses solely on the public functions and methods of a package, ensuring reliable code usage as it mimics how consumers would interact with the package. This approach is particularly useful during code refactoring, as it helps maintain stability when internal implementations change. Conversely, white box testing provides access to internal methods, allowing for more granular testing but potentially leading to brittle tests that break with internal changes. While black box testing is preferred for its robustness, there are scenarios where white box testing can simplify the testing process. Ultimately, the choice between these testing methodologies depends on specific needs, with the overarching goal being to facilitate efficient development and maintenance of high-quality code.