I read this brief article at codinghorror about how bad developers are at testing. I am of the same opinion that developers are mostly not that good testers but then again they have to develop as well :). All the testers have to do is test but the developers have a lot more stuff to think and do. To ask them to test as well as develop is perhaps asking too much. but that said, I think its absolutely empirical that developers test what they develop or perhaps even before they develop :). But that requires acknowledgement and realization of the importance of testing both at the developer and the project manager level. There must be considerable time available for developers to test what they develop otherwise, the Customer Support and the Testing guys will have their work cut out.