Legacy Coderetreat: Episode 12 – Unit Testing on Legacy Code – Codecast

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Unit Testing on Legacy Code – Codecast

Blog post series

This blog post is part of a series about legacy coderetreat and legacy code techniques you can apply during your work. Please click to see more sessions about legacy code.


This is a codecast in Java.

In the previous episodes we reach the moment when we extracted one simple class. We used the The Rule of Three and pure functions. This newly extracted class is covered with characterization tests. But that is not enough, we want to continue adding other types of tests to understand the system better.

This is why during this episode you will see how to add unit tests to code extracted from a legacy code class. These tests have a small granularity level than the characterization tests we already have. This is the moment to dive more into details.

See this video to understand how you can document the current state of the system, by unit testing on legacy code.

Read here more about this concept in my blog post.

We started with a class having non-public methods. The purpose of this session was to start covering the class with tests. In this moment we have short and clear unit tests, written in isolation of any slow dependencies. These tests are fast and we need to run then any time we will change the production code, to make sure we do not introduce defects.

In the same way as shown in the last blog posts, we can extract pure functions, extract classes and then cover these classes with unit tests.


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