As I recall the TDD mailing list has some background on the use of the word "unit", it goes WAY back, I believe it goes back to the mainframe/ punch card era. R

As I recall the TDD mailing list has some background on the use of the word "unit", it goes WAY back, I believe it goes back to the mainframe/ punch card era. Regardless, I think it roughly translates to C's notion of the unit of compilation. Which is obviously not what people really mean these days, but the phrase stuck. The early Xp'ers even found it an issue back then. For a while people tried to push the term "micro tests", but that didn't really take off. I agree with Gerard Mezaros and Martin Fowler and typically follow their (very mainstream) definitions on this stuff. Integration and functional testing have their own ambiguities too, it's definitely a frustrating situation to not have solidly defined foundational terms.