The Unit testing is a process of testing the smallest piece of code referred to as a unit that can be logically isolated in a system. This is mainly focused on the functional correctness of standalone modules.

The unit can be almost anything you want it to be – a specific piece of functionality, the program, or the particular method within an application. Smaller the unit, better it is. Where the smaller tests usually give you a much more granular view of your production, the code is performing. And also, your tests can run faster if they are small. So, it is also micro-level of software testing.