Usability testing is a technique used in user-centered interaction design to evaluate a product by testing it on users. This can be seen as an irreplaceable usability practice, since it gives direct input on how real users use the system.This is in contrast with usability inspection methods where experts use different methods to evaluate a user interface without involving users.
Usability testing focuses on measuring a human-made product's capacity to meet its intended purpose. Examples of products that commonly benefit from usability testing are foods, consumer products, web sites or web applications, computer interfaces, documents, and devices. Usability testing measures the usability, or ease of use, of a specific object or set of objects, whereas general human-computer interaction studies attempt to formulate universal principles.
Goals of usability testing
Usability testing is a black-box testing technique. The aim is to observe people using the product to discover errors and areas of improvement. Usability testing generally involves measuring how well test subjects respond in four areas: efficiency, accuracy, recall, and emotional response. The results of the first test can be treated as a baseline or control measurement; all subsequent tests can then be compared to the baseline to indicate improvement.
Performance -- How much time, and how many steps, are required for people to complete basic tasks? (For example, find something to buy, create a new account, and order the item.)
Accuracy -- How many mistakes did people make? (And were they fatal or recoverable with the right information?)
Recall -- How much does the person remember afterwards or after periods of non-use?
Stickiness -- How much time he/she spends
Emotional response -- How does the person feel about the tasks completed? Is the person confident, stressed? Would the user recommend this system to a friend?
To assess the usability of the system under usability testing, quantitative and/or qualitative Usability goals (also called usability requirements) have to be defined beforehand. If the results of the usability testing meet the Usability goals, the system can be considered as usable for the end-users whose representatives have tested it.
What usability testing is not
Simply gathering opinions on an object or document is market research or qualitative research rather than usability testing. Usability testing usually involves systematic observation under controlled conditions to determine how well people can use the product. However, often both qualitative and usability testing are used in combination, to better understand users' motivations/perceptions, in addition to their actions.
Rather than showing users a rough draft and asking, "Do you understand this?", usability testing involves watching people trying to use something for its intended purpose. For example, when testing instructions for assembling a toy, the test subjects should be given the instructions and a box of parts and, rather than being asked to comment on the parts and materials, they are asked to put the toy together. Instruction phrasing, illustration quality, and the toy's design all affect the assembly process.