Welcome to the first lesson of our course on Test Driven Development (TDD) in Java using JUnit. TDD is an iterative software development process where tests are written prior to developing the actual functionality. This approach helps developers focus on the requirements first, leading to more reliable and maintainable code.

In this lesson, we'll introduce you to the essential elements of TDD, including the Red-Green-Refactor cycle, which serves as the core structure of this methodology. We'll be utilizing tools specially suited for Java: JUnit, a popular testing framework that is robust and integrates well with Java. These tools are excellent for defining and running tests in Java. Let's start by investigating TDD’s core components with a hands-on example.

The TDD process begins with writing a test that fails, marking the "Red" phase. This step allows you to crystallize what the code should achieve before writing the actual implementation. Let's write a test for a sum method that should eventually add two numbers.

Create a file named MathTest.java in the tests directory:

This test script:

• Uses @Test to denote a single test case.
• Instantiates a class.