Usability testing is the most basic and useful method of testing the usability or ‘ease of use’ of a website or application. Usability testing simply involves asking a group of users to perform certain tasks and observing what the users do, if they are successful or where they have difficulties. Usability testing is the best way to determine if a website works and how to improve it. There are several Usability Testing Guidelines that should be followed:
Usability testing reveals how users react to a website or application design. Usability testing can occur throughout the design and development cycle, but it is most important to test before the design of the website or application is finalized and developed.
The first phase of usability testing enables designers to evaluate user responses to the system design and make changes to the design before it has been committed to code. By making a simple paper prototype of the website or application, the flaws in the design are revealed before money and time are spent on implementation. At this early stage it is possible to make major changes to the user interface, redesign the functionality, and add or remove features before it has been coded. Because user testing shows how users actually use the website, the initial testing results help guide the design and development team throughout the entire development cycle. In fact, early usability testing will reduce the amount of development time needed because the testing results will reveal that some features are unnecessary or will discover that some processes can be streamlined. “Testing one user early in the project is better than testing 50 near the end.” 
Early usability testing is vital to ensure a website’s success and proves to the design team that users do not behave and think like a developer, thus they do not use the website in the same way.
5 is the Magic #
Usability testing with 5 users ensures the maximum cost to benefit ratio. Testing costs increase with each additional test user and it has been proven that there is little additional benefit to having more than 5 test users throughout the same test study. It has been found that the best usability test results are derived from testing no more than five users per test and running many small tests throughout the design and development cycle.
User testing with 5 users will ensure finding the maximum amount of usability problems and design issues and spending the minimum amount cost.
Usability testing should not stop after a single round of testing. Usability testing is an iterative process of testing 5 users, fixing the problems uncovered, and then testing the revised design with 5 new users. In the second round of testing, with the first problems fixed, the test users will find new problems that they could not have encountered during the first round of testing. 
The best use of resources is to run many small user testing rounds and revise the design between each round so the usability flaws are corrected as they are identified. “User testing followed by single design iteration improves measured usability by 38% on average.”  It is most important to do many rounds of user testing throughout the development cycle in order to maximize usability and minimize the costs of development.
Sit Back and …Watch
In order to evaluate the usability of a website or application, designers and developers must closely watch individual users as they perform tasks with the user interface. The usability testing process involves asking the users to perform specific tasks with the design in a calm and relaxed testing environment.
A usability test consists of 5 to 10 tasks within a 60 to 90 minute session. It is most important to establish very clear success criteria for each task. Tasks should be designed to answer a specific question and should represent the most common goals of the website or application, such as making a purchase or setting up an account.
The usability testing environment should be casual and comfortable. Any design team member can facilitate the user testing, although they must not be too controlling and rigid. If the test users are nervous they will not have the confidence to behave naturally when testing. Also, it is important to let the users solve any problems they experience or encounter on their own and not provide any direction or assistance. Often, the test users may request guidance, although it is crucial to allow them to resolve problems in their own way so their thought process is not interrupted. It is best to have all design and development team members observe the user testing results because it provides valuable information concerning the website or application design functionality. 
Just sit back and watch. The usability testing process must include specific usability tasks facilitated in a relaxed environment. Usability testing shows the design and development team how users will use the website or application by observing the users succeed or fail when completing a specific task. “If you want to know whether your website is easy enough to use, watch some people while they try to use it and note where they run into trouble. Then fix it, and test it again.” 
Usability Testing is easy, informative and invaluable
Usability testing is an easy, informative and invaluable method of assessing the ‘ease of use’ of a website or application because it saves time and money by discovering the flaws in the design before development. There are 4 easy guidelines to follow when conducting usability testing:
Test early in the design and development process to avoid design flaws and failings.
Only 5 test users are needed for a round of testing.
Test often with many rounds of testing between design changes.
Ask the test users specific action questions and watch their responses.
Nielsen, Jakob. “The Most Important Usability Activity.” NN/g Nielsen Norman Group. July 16, 2012. http://www.nngroup.com/articles/the-most-important-usability-activity/.
Rees, Damian. “Improving your website usability tests.” Smashing Magazine. January 8, 2013. http://www.smashingmagazine.com/2013/01/08/improving-your-website-usability-tests/.