Test-Driven Development by Example

Blurb

Test Driven Development: By Example is a book about a software development technique by Kent Beck.
Beck's concept of test-driven development centers on two basic rules:
Never write a single line of code unless you have a failing automated test.
Eliminate duplication.
The book illustrates the use of unit testing as part of the methodology, including examples in Java and Python. One section includes using test-driven development to develop a unit testing framework.