After taking a quick look at JaCoCo in class I wanted to learn a bit more about it. This article is an introduction to using JaCoCo and gives some good examples.

The article explains that when you write tests there are some criteria to consider:

  • We want to make sure that the parts of the code that are best tested are the parts that are most likely to contain bugs.
  • We want to focus our tests on parts of the application that are critical, the parts where bugs are most likely to lead to a bad outcome for our customers.
  • We don’t want to write tests that repeatedly cover the same areas of the code while ignoring other parts of the code.

You can find which parts of the code are the most likely to have bugs by finding the most complex parts. A common way to do this is using cyclomatic complexity (check the article for the algorithm).

JaCoCo measures code coverage, can report on the complexity of each method, and can tell you how much complexity is untested. In the article a lot of the things we covered in class are repeated, but it helps to see it again to reinforce the concepts and also to reference for the future. While we spoke about it in class, a lot of the things that are said are not recorded anywhere.

The article also brings up the use of JaCoCo to measure complexity. After getting as much code coverage as possible you can refactor your code if the complexity score is too high. In the example they reduce a method’s complexity from 21 points to 9 points. That just goes to show how useful JaCoCo is. After reducing complexity and improving code coverage you can be confident your code is ready for a code review.  

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