Unit Tests as a Design Tool: Increase Coverage and Improve Your Code

The benefits of using unit tests in your code cannot be overstated. Not only do they serve as a powerful refactoring tool, but they also act as a design tool to improve the quality of your code. If your application currently lacks unit tests, now is the time to start the journey toward 100% unit test coverage.

Unit tests as a refactoring tool

Without unit tests, refactoring can be a tedious process. It typically involves attempting to run or compile your code, reading a single stack trace, and fixing a single bug. With unit tests, however, this process becomes much more efficient. When multiple unit tests fail, you can fix multiple bugs simultaneously, saving you significant time.

Unit tests as a design tool

To convince you further, learn about why integration tests are a scam and why you should write unit tests instead. Another favorite reason I love unit tests is that they are a fabulous design tool.

It's difficult to write simple tests for complicated code.

- John Solly

In addition to their usefulness as a refactoring tool, unit tests also serve as an excellent design tool. Writing simple tests for complicated code can be difficult, so the implementation probably has room for improvement. I followed the TDD approach for my blog "blogthedata.com" and found missing coverage across several files. 

Name                                    Stmts   Miss  Cover   Missing
---------------------------------------------------------------------
blog/templates/blog/categories.html        42      2    95%   35-36
blog/templates/blog/home.html              47     19    60%   33-52
blog/templates/blog/search_posts.html      50     19    62%   36-55
blog/templates/blog/user_posts.html        37     19    49%   20-39
---------------------------------------------------------------------
TOTAL                                    1164     59    95%

I discovered that I had duplicated the same pagination code across multiple files in my application. Rather than writing separate tests for the same logic in various locations, I chose to refactor the code by moving it into a separate file and utilizing Django's {% include %} tag to inherit it into the four templates.

By taking this approach, I achieved 100% code coverage after re-running my tests, without having to write a single additional test. This is a great example of how unit tests can be used as a design tool to improve the quality of your code and make it more maintainable.