I taught evolutionary design in person to about 200 programmers this year.1 In the 15 years that I’ve been doing this, I’ve spoken with confused programmers who felt unsure how to use dependency injection to improve their design. I tend to notice this confusion more often among the programmers who have “some experience” practising test-driven development—say, 6 months to 2 years. I’d like to share a few short pieces of advice, and if this advice leads you to ask some follow-up que...
