"Test coverage and post-verification defects: A multiple case study" by Audris Mockus, Nachiappan Nagappan, Trung T. Dinh-Trong, Proceedings of the 2009 3rd International Symposium on Empirical Software Engineering and Measurement, October 2009

Available at the ACM digital library at: http://portal.acm.org/citation.cfm?id=1671248.1671276&coll=ACM&dl=ACM&CFID=80887391&CFTOKEN=40233171

The paper addresses a very fundamental and important question about program testing -- Does increased code coverage make tests better? To address this question, the authors perform a thorough and detailed analysis of two large and dissimlar code bases at Microsoft and Avaya, Inc.

Their conclusion is that increased coverage does in fact lead to better tests, where "better" means that the tests with more coverage decrease the number of field-reported problems in the deployed software. They support their conclusion with a detailed description of their methodology and observed results.