The Recipe
You can follow many different approaches to testing. You can test the rough functionality first and then selectively refine it. You can select a functional, architectural, or design section and dive into it thoroughly. There is value in taking a more ad hoc or random approach akin to manual exploratory testing. Yet another approach guides your testing by metrics, such as defect densities, complexity, or criticality.
This section details an approach, visualized in Figure 3-1, that I have found useful in driving toward high coverage, independent of how you select the code or functionality to test. The approach favors deep over broad testing. It works well when taking a test-driven approach to new code, but also applies well when reproducing bugs, enhancing existing code, or bringing existing code under test.
