You cannot test your own design by looking at it. You know where everything is, you know what the labels mean, and you know what happens next. That knowledge is precisely what your users do not have.
Testing swaps your judgement for evidence. Put the design in front of someone who has never seen it, give them something to do, and watch where they stall. Two questions are worth keeping apart: can people work out how to use this, and can people use it at all. The first is usability. The second is accessibility, and a design can sail through the first while failing the second completely for anyone on a screen reader or a keyboard.
Test before you ship, then again after. Real traffic finds things a lab never will.
Usability Testing
Give someone a task, not a tour. "Book a room in Lisbon for the 14th" — then stop talking. Silence is the instrument. The moment you explain what a button does, you have destroyed the thing you were measuring.
Record behaviour, not opinion. Where did the cursor hover? What did they read twice? For each task, note whether they finished, how long it took, and the point at which they went wrong.
Moderated sessions let you ask why. Unmoderated tools buy more sessions for less money and no follow-up questions. Run moderated when you do not yet know what is broken; unmoderated when you have one flow to compare.
None of this needs a finished product. A clickable prototype — paper, even — finds the same dead ends weeks before anyone builds them.
Five to eight people, watched properly, will show you most of it.
- Usability (User) Testing 101 — article
- Usability Testing Tips and Examples | Google UX Design Certificate — video
Accessibility Testing
Unplug the mouse. Move through your product with Tab, Shift-Tab, Enter and Space. If you cannot reach a control, or cannot see which element has focus, you have found a defect before any tool has run.
Then run an automated checker — axe, Lighthouse, whatever sits in your pipeline. It finds missing alternative text, low contrast, unlabelled form fields, broken heading order. It will not find everything: a machine can tell whether alt text exists, not whether it is useful. A clean report is the floor, not the ceiling.
The rest needs a screen reader, and better still, someone who uses one every day. Work to WCAG, Level AA — and check which version your jurisdiction and your biggest customers name before you promise anything.
Accessibility retrofitted at the end is a rebuild. Handled from the start, it is mostly picking the right element and labelling it properly.