Unit testing is the sort of testing that is normally close at heart for developers. The primary reason is that, by definition, unit testing tests well-defined parts of the system in isolation from other parts. Thus, they are comparatively easy to write and use.
Many build systems have built-in support for unit tests, which can be leveraged without undue difficulty.
With Maven, for example, there is a convention that describes how to write tests such that the build system can find them, execute them, and finally prepare a report of the outcome. Writing tests basically boils down to writing test methods, which are tagged with source code annotations to mark the methods as being tests. Since they are ordinary methods, they can do anything, but by convention, the tests should be written so that they don't require considerable effort to run. If the test code starts...