Test Driven Development is the practice of development by creating tests. This document explains the basics of this methodology.
For this example, we're going to try to write a method that returns the primitive true. Our first step is
to write the test method. This exercise is useful because it helps us define our API.
Here we can see that we've written two tests. The first test checks to see if the method returns the right type. The desired type is a boolean. The second test checks to see if it returns the correct boolean, true. For more complex examples, you may want to write tests for specific cases or different classes of input.
Run your tests. Your new test should fail. If your code doesn't compile, create the method, but don't actually fill in the method yet. If you must return something, typically "false" or "null" or "0" types of values should be your default return values before the method is implemented. You can see the method here.
Try to fill in the method with some code with the goal of passing your tests. This was the assessment.
If your tests pass, then continue! If they don't, then continue fixing your code and running your tests until they pass.
Your code may pass the tests, but it may also be hard to read, or there might be a good reason to move code around. For example, you may want to split your code into smaller pieces for better code reuse. Refactor your code and run tests to make sure it still works. If you ever need to refactor your code in the future, then you have tests so you know you haven't broken anything.
While adding/removing features or otherwise changing code, you can continue to add and rerun tests to ensure your code works as expected.