Objectives of Usability Testing

When testing an application, we always keep three questions in mind.

• What should the test subjects be doing at each point to get their tasks accomplished?

• What are the test subjects doing at each point, and if they aren't doing the right (or optimal) things, what are they doing?

• What are the similarities and differences between the mental model of the system that the subject is forming and the mental model that the designer intended?

Finding the answers to these questions can happen at several points in the process of designing a system.

When is the right time to test an application? It depends on the size. We'd probably want to test a subset of the total functionality of a very large application in stages throughout the design and implementation process. For smaller applications, it just makes sense to test when design and implementation is nearly complete.