Code coverage

Code coverage is a metric (in percent) that calculates the number of code elements that get called by tests, divided by the total amount of code elements. Code elements can be anything, but lines of code, code blocks, or functions are common.

Code coverage is an important metric as it shows you what parts of your code are not covered by your test suite. I like to watch the code coverage before I finish a code change as I often forget to write tests for edge cases such as exception handling, or more complex statements such as lambda expressions. It's no problem to add these tests the moment you are coding – it's much harder to add them later.

But you should not focus on the absolute number as code coverage itself says nothing about the quality of the tests. It's better to have 70% code coverage with high-quality tests than 90% percent code coverage with low-quality tests. Depending on the programming language and frameworks you use, there might...