You chose this option:
Start by reading the requirements carefully. When you’ve understood them, write code to fulfill the requirements. When you think everything is working, write a test case that checks the code works. Continue adding test cases one by one checking each passes as you finish it.
This is not really a test-driven approach, is it? By writing the solution code first you lose the opportunity for the tests to influence your design. You may write more code than is needed to fulfill the requirements since you have no tests to guide you. In the end your tests may become tightly coupled to your implementation and difficult to maintain as the design evolves. I’d recommend a more test-oriented analysis of the requirements. Take a look at Option B for more information.