Usability testing is evaluating a product by letting users try it out.

You can divide usability tests by the location they are done:

• Remote usability testing: testing is done remotely with little or no surveillance. Digital products are tested on tester's own computer and physical product must first be mailed.
• Street usability testing: testing is done on the spot where you encounter a potential user e.g. asking people to try your mobile app on the street or asking people to try your web store on your laptop in a coffee shop.
• Lab usability testing: testing is done in a usability laboratory with video recording, users are usually recruited beforehand and tests are scheduled.
• Contextual usability testing: testing is done where users will be using the product e.g. warehouse software is tested in a warehouse. There might be real world conditions and restriction that other usability testing types do not notice.

Start usability testing earlier than you would think. You should start by testing your paper sketches on the real users.

Is the navigation structure and interaction process understandable?

Plan and prioritize key questions you are testing for. You should create concrete tasks to give to the users. These tasks should be planned to give answers to the key questions.

Tasks

Tasks are the missions you give to the user.

Post a status update on the site.
Find and buy the cheapest umbrella.

First task should be to learn the context users arrive to the website e.g. task to search online for a house in their neighbourhood with given price range.

Second task should be easy and broad so user feels empowered to do whatever they want.

Free roaming tasks. Few tasks should be so that you can leave the room and let user roam around the website freely. You can find real gems in there.

Test Situation

Be extra nice to the user. Start normal usability testing situation by stating that you are testing the product, not the user. Avoid being controlling.

Only one person should spectate the test. Additional people create unnecessary stress for the user.

Record everything. Record the user and the screen. Tell this to the user.

Make them speak. Ask them to say out loud what they are thinking as they are using the product. Do not ask something every 30 seconds.

Let them make mistakes. If user does something "wrong", just spectate where this leads. But note that when user does something wrong, problem is not the user, it is the product and design. You might get to test few known unknowns but you effectively hide all unknown unknowns.

Evaluate your product in competition environment. Ask if the tester has used any similar products. If they are web based, ask them to show them to you. Consider including few tasks working with a competing product to see how user feels about them. Consider hiding what service we are really testing. The tester is more honest.