Interesting implementation of contract first development model.

DevLabs Code Contracts

http://msdn.microsoft.com/en-us/devlabs/dd491992.aspx

Microsoft offers language-agnostic coding technology

Code Contracts enables "design by contract" programming for .Net

http://www.infoworld.com/article/09/02/24/Microsoft_offers_language_agnostic_coding_technology_1.html