In this interview filmed during RubyFringe 2008, Luke Francl explains his position towards testing. While supporting unit testing, he thinks testing is not going to reveal all application defects. Development teams should also practice code reviews and usability tests which are likely to discover bugs not visible though other methods.
Debate sprang up at JAOO '07 around Bob Martin's assertion that "nowadays it is irresponsible for a developer to ship a line of code he has not executed in a unit test." In this InfoQ video, he debated with Jim Coplien on this and other topics, including Design by Contract vs. TDD and how much up-front architecture is needed to keep a system consistent with the business domain model.
Ron Jeffries' upcoming book looks at how tracking "Running Tested Features" is the essential element of Agility, from which all other practices and activities necessarily follow. Deborah Hartmann interviews Ron who takes to the whiteboard to explain how, when supported by XP's "simple design" practice, RTF helps teams deliver consistently without building up costly technical debt.