“People also underestimate the time they spend debugging. They underestimate how much time they can spend chasing a long bug. With testing, I know straight away when I added a bug. That lets me fix the bug immediately, before it can crawl off and hide. There are few things more frustrating or time wasting than debugging. Wouldn't it be a hell of a lot quicker if we just didn't create the bugs in the first place?”
Martin Fowler (2002) as cited in Evolutionary Design: A Conversation with Martin Fowler, Part III by Bill Venners, November 18, 2002.
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Martin Fowler 18
British programmer 1963Related quotes

[7238@jpl-devvax.JPL.NASA.GOV, 1990]
Usenet postings, 1990

Nicholas Negroponte: A 30-year history of the future http://www.ted.com/talks/nicholas_negroponte_a_30_year_history_of_the_future, July 2014, TED Talks (about 13:40 into 19:43 video).
A 30-year history of the future, TED Talk (2014)

Focus Magazine No. 43 (23 October 1995) http://www.cantrip.org/nobugs.html <!-- pages 206-212 -->
1990s

“Program testing can be used to show the presence of bugs, but never to show their absence!”
Dijkstra (1970) " Notes On Structured Programming http://www.cs.utexas.edu/users/EWD/ewd02xx/EWD249.PDF" (EWD249), Section 3 ("On The Reliability of Mechanisms"), corollary at the end.
1970s
Variant: Program testing can be a very effective way to show the presence of bugs, but it is hopelessly inadequate for showing their absence.

“Testing shows the presence, not the absence of bugs”
Dijkstra (1969) J.N. Buxton and B. Randell, eds, Software Engineering Techniques, April 1970, p. 16. Report on a conference sponsored by the NATO Science Committee, Rome, Italy, 27–31 October 1969. http://homepages.cs.ncl.ac.uk/brian.randell/NATO/nato1969.PDF Possibly the earliest documented use of the famous quote.
1960s

[199710050130.SAA04762@wall.org, 1997]
Usenet postings, 1997