Really Sassy — cool — in .NET or in PHP as well?

Working on some complex software in current dayjob, and the complexity can only be managed if the shiznit works. When it fails, it tends to do so opaquely — is it the database? is it the sessions? is it the object, if so which one? is it a dumb html or javascript error? What I want is sets of test data that will tell me what is working.