Every template I sell goes through the same three tests, and none of them are about how it looks.
The first test is the boring afternoon. I install it on a fresh WordPress with no plugins, add sixteen items of fake content with stupid-long names, and try to break the layout. Long titles, missing images, one-line paragraphs. Most templates look great with three tidy cards and fall apart with twelve messy ones.
The second test is the borrowed laptop. I keep a 2019 machine around specifically to open each template on. If it takes more than two seconds to become usable on that laptop, I cut something until it does.
The third test is someone else using it. I hand it to a friend who does not design and watch them try to change the accent colour without asking me. If they have to ask, the settings are wrong.
That’s it. No automated screenshot suite, no headless browser farm. Just content I am embarrassed by, a slow computer, and a person who does not care about my grid.