The primary goal of unit testing is to take the smallest piece of testable software in the application, isolate it from the remainder of the code, and determine whether it behaves exactly as you expect. Each unit is tested separately before integrating them into modules to test the interfaces between modules. Unit testing has proven its value in that a large percentage of defects are identified during its use. If you are looking for commercial testing tools, SpiraTest is the most powerful and affordable test management solution on the market today. Ranorex Functional Test Automation Tool for any technology.
At this level of testing, tools target specific programming languages. The most famous unit testing tool is Junit, a open source framework to write repeatable tests. It was the base of the xUnit architecture for unit testing frameworks that has been used in many programming languages.