Test-driven design can be daunting at first. This book presents a moderately complex task - write a program that can read a mathematical expression like 2 + 3 * 5 and return its result. The author explains each step with both tests and production code until the program can handle decimal numbers, multiple levels of parentheses and even symbols (like in x + 3). This is a code-heavy, hands-on book; just reading it without writing the code yourself might not provide the full benefit.