JUnit 4.3.1

1. JUnit and its benefits 
   Unit is an open source framework that has been designed for the purpose of writing and running tests in the Java programming language. JUnit was originally written by Erich Gamma and Kent Beck.
       
2. Downloading and installing JUnit 4.3.1
   In this section, downloading JUnit 4.3.1 address and installation steps have been given. You can download this in your system and test your program whether it is functioning well or not.
     
3. Writing and testing
   This section starts with a simple example that will illustrate the basic concepts involved in testing with JUnit. In this section, we will be creating a java file named Calculator.java which has a method named sum() which takes two int parameters and return addition of these two numbers. So here we have to check whether this method is functioning well in all the conditions or not.