Flask Web Development, 2nd Edition

Chapter 15. Testing

There are two very good reasons for writing unit tests. When implementing new functionality, unit tests are used to confirm that the new code is working in the expected way. The same result can be obtained by testing manually, but of course automated tests save time and effort because they can be repeated easily.

A second, more important reason is that each time the application is modified, all the unit tests built around it can be executed to ensure that there are no regressions in the existing code; in other words, that the new changes did not affect the way the older code works.

Unit tests have been a part of Flasky since the very beginning, with tests designed to exercise specific features of the application implemented in the database model classes. These classes are easy to test outside of the context of a running application, so given that it takes little effort, implementing unit tests for all the features that exist in the database models is the best way to ensure at least that part of the application starts robust and stays that way.

This chapter discusses ways to improve and extend unit testing to other areas of the application.

Obtaining Code Coverage Reports

Having a test suite is important, but it is equally important to know how good or bad it is. Code coverage tools measure how much of the application is exercised by unit tests and can provide a detailed report that indicates which parts of the application code are not being tested. This information ...