How to test a product?

1. Requirements based testing - Test it based on Product Requirements doc
2. Parallel testing - Test it against competitor and peer products
3. Scenario testing - Assume different scenarios for different kinds of end users.
4. Usability testing - Based on usage of the product
5. Function testing - Based on functionality
6. Fault Injection - Inject problems
7. Stress testing - Stress it out
8. Performance testing - metrics
9. Regulations - specs

A blog article on all possible test scenarios for a stapler is available in the following location:
http://www.testingreflections.com/node/view/928