I think the question should be not testing to development but total completed work. It takes so many hours to do the job. Since you are purchasing from an outside contractor your concern should be completed, bug free, fully functional solutions. No matter what the contractor does you owe it to yourself to do full acceptance testing -- does it do what the functional specs says. You have to do this testing unless your contract gives you an iron clad "It Works - Bug Free" or you don't pay. In that case I would lots of time testing to be sure you couldn't find anything that would hold up my final payment.

Having said the above I have a personal example, a very large application that two of us produced. I created protypes of system, associate coded and I tested his work. We spent 2 years on the project and the client later said it was the must bug free system he had seen in his 15 years in the software industry.

The quality of the testing work is more important than relationship to the developement time. I believe teams of developers and testers working together do the best overall best quality for the final product.