Commercial off the shelf Testing
If the COTS product/application fully meets the business requirements, the need for testing is certainly lowered. However, if modifications to presentation or functionality are made, a more traditional test approach will be required.
Even if used 'out of the box' with no modifications, you still need to consider the following:-
Integration - Where you are integrating a COTS product with other systems, integration testing is clearly required. The goal of testing is not to verify the functionality of product, but to assure information can be shared between them and correctly sent and received.
Performance - Implementing a COTS solution does not guarantee sufficient performance of the product. Whether your intended customer is in-house or external, performance testing is required to ensure your environment is set-up correctly to met service level agreements.
Configuration - Most COTS products come with a vast amount of configuration. Whether its: workflows, security, etc.., this will still require testing to ensure the application is set up correctly to meet your business needs.
It might be tempting to dismiss the need for testing, but it's just not that simple. Take the time to analyze the product/application so that you ensure the correct levels of testing are carried out. And then, after you test, all there's left to do is hope that it works : - ).