Wha? I'm not even sure if you read my comment before replying! To restate: the only reason you ever modify the method of drawing a line segment is to change the sequence of emitted API calls (or output XML, or something). Therefore a unit test for that method that nails down the sequence is useless. Or is it me who's missing your point?

The cost to fix a defect you have just introduced is typically a few minutes; the cost to fix the same defects a few days, weeks or months later can be orders of magnitude bigger, rising fast with the magnitude of the delay.

For the record, I don't buy that either. I can fix a bug in our webapp in a minute after it's found, and have done that many times. Why do you believe the cost rises, anyway? Maybe you're living in a different "world" after all? :-)

Thanks for the links about Eclipse, they don't seem to prove your original point but they're still interesting.