Test-driven modeling

For the last recipe in the book, I'd like to present a recipe that is central to my view of the integration of modeling and Agile methods. The archetypal workflow in Agile software methods is test-driven development (TDD), in which you do the following:

    Loop
        Write a test case
        Write a bit of code to meet that test case
        Apply test case
        If (defect) fix defect;
    Until done;

It's an appealing story, to be sure. Each loop shouldn't take more than a few minutes. This is a key means in Agile methods to develop high-quality code; test incrementally throughout the coding process.

TDD aligns with this law of Douglass:

The best way not to have defects in your system is to not put any defects into your system....