When you have a legacy product that has been around for over 10 years and it is written with old technologies and has no automated tests, how do you improve quality? Sometimes the best solution is to rewrite it! That was the situation we were in with a product written with JBOSS. It had become difficult to maintain and debug so we decided to rewrite it using the Spring Boot framework, and add unit and integration tests as we were doing it. This is not a simple undertaking and it's still a work in progress; but I feel we made the right decision. As not many of the developers had much experience with writing unit and integration tests, I wrote up the guidelines shown below. These have been written for a Java based Spring Boot project that uses the JUnit framework to write the tests, but are general enough to apply to most languages and frameworks. Guidelines: Test the behaviour of the class; not its implementation. Don’t test implementation details; e.g. priv