A simple example using JUnit
https://technologyconversations.com/2013/12/20/test-driven-development-tdd-example-walkthrough/

Another simple example can be found at the end of:
https://www.guru99.com/test-driven-development.html 

Kent Beck’s book on Test-Driven Development starts with a short example
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnx0ZXN0MTIzNHNpbTQ2NXxneDpiYTJmYWIwYTAyOGJiZmQ