Diffblue Cover

Diffblue Cover generates unit tests for Java applications without you having to write them. It analyzes the code, works out what it does and produces tests that lock in that behavior, which is very useful before you change an older codebase. Unlike general chat assistants, it uses reinforcement learning and runs the tests it creates to confirm they compile and pass. It can run inside the IDE or in a CI pipeline, so test coverage grows as the project does. Diffblue has a free community option and paid enterprise plans. It is a strong fit for large Java shops with legacy code and thin test coverage.