Modern C++ Programming with Test-Driven Development

10.3 Unit Tests, Integration Tests, and Acceptance Tests

TDD is a programmer practice to help you incrementally drive the design of code. You’ve learned how to use it to verify small bits of C++ logic by writing unit tests, which in turn allows you to continually shape the design of the code at will.

For the purposes of this book, ​unit​ means a small piece of isolated logic that affects some systematic behavior. The word ​isolated​ in the definition suggests you can execute the logic independently. This requires decoupling the logic from dependencies on things such as service calls, APIs, databases, and the file system. (Technically, independent code should also be decoupled from any other code, but a pragmatic approach suggests that it’s not ...