Test smells are considered bad practices for developing the test code. Their presence can reduce the test code quality, thus harming software testing and maintenance activities. Software refactoring has been a key practice to handle smells and improve software quality without changing its behavior. However, existing refactoring tools target production code with very different characteristics than test code. Despite the research invested in test smell refactoring, little is known about whether current refactorings improve the test code quality. This thesis proposal presents our research to help developers decide when and how to refactor test smells through a machine learning-based approach. First, we aim to mine refactorings performed by dev...