I meant it figuratively. Safety and security certification at high levels often required that every module and function be tested. That was on top of black box testing and pen testing. Some practitioners added fuzz testing, path-based, symbolic, combinatorial, etc.

So, not literally exhaustive. They just covered every function, feature, interface, and combination that might trigger a bug.

Although, some rare folks did do literally- exhaustive testing of algorithms and FSM’s on 8-bit MCU’s since they had 256 values per variable. Others and I put timers on loops to force it to be terminating and just analyzed those cases. One could use exhaustive testing in the small to justify modeling a function with a specific formula. If you have several of those, then methods like Cleanroom Software Engineering let you semiformally verify the correctness of upper layers.

So, there’s some stuff like that which was used on an ad hoc basis. Most just tested values and combinations likely to trigger bugs since they were in ranges that cause effects.