Code Coverage

Managers love numbers. The concept of code coverage, a term for how much code is unit-tested, is one that tickles the typical manager’s number fixation but ultimately leaves a bad taste when used for anything but educational purposes.

Code coverage

More specifically, code coverage is a measure of the percentage of code that our unit tests execute. We can find tools that do the dirty work of taking the measurements. Emma (which we show briefly here—it’s a free and easily installed Eclipse plugin) and Cobertura are examples of code-coverage tools.

Example: Coverage class

Imagine that we have a Coverage class containing only one method named soleMethod(), and that soleMethod() contains a single non=conditional statement. If we run a unit test that calls soleMethod(), the statement is executed. The code coverage for soleMethod() and the class (since Coverage has no other methods), is 100%. If we run no unit tests that call soleMethod(), the code coverage for Coverage is 0%.

Next, consider that soleMethod() contains an if statement with a single simple conditional and the body of the if statement is a single statement. Here’s an example of this code scenario: