Unit tests become more valuable when they test units of work rather than units of code. By treating tests as small simulations — setting a known system state, simulating inputs, and verifying outputs against functional requirements — developers can write behavior-focused tests that remain robust even when implementation changes. This approach, rooted in BDD principles, is especially relevant for embedded systems where hardware dependencies make pure isolation testing fragile and often meaningless. Treating the system as a black box ensures tests validate what the system does, not how it does it.
