Usability testing could have happened in many different ways during your project lifecycle. Usability Test is still the best method of ensuring your product users in achieving their goal EASILY and QUICKLY.

Usability test?
This is a way that you can test your product to see how easy is to use with real users. UXer should ask users to complete tasks and should be observed by researcher/UXer to see where they clash problems and experience confusions.
Then you should check the most common problems and put high priorities to overcome these ability issues.
If I want to describe Usability, I should call it a method to evaluate how easy the product is to use. Real users should take a test to measure how ‘useable’ or ‘sensory’ a product/web easy it is for them (Users).
The usability test is one of the new methods that we can’t compare it with other tests/methods. Previously Product Owner/Company Owner was guiding design team to change most of the bug testing, acceptance testing.

Comparative Usability Testing
One of the most common tests is comparing one product to another product. The comparative test is commonly used to compare product against or competitors.
It can be used to compare two designs to establish which provide the best UX as well.

Explorative Usability Testing
This is the pre-design test that might help to UXer to find/highlight the market’s gap that could be a very big point for the product to beat its competitors.
Explorative Usability Testing can establish content and functionality a new product should include meeting the needs of users.

Usability Evaluation
Usability Evaluation is on the pre or post launch to test the new/updated product. UXer should introduce users to the product to ensure it is sensory to use and provides a positive user experience.
The goal of Usability Evaluation is to highlight and fix any potential issues before the product launched.