Sorry, I'm not familiar with the GUI tester.

r? @jsha

r? @notriddle

I'm not very familiar with how this tool works, either.

r? @jsha

I'm not sure if @jsha is either. Oh well, we'll see. :)

BTW, this does seem like a reasonable change to me. If you're using a "headed" browser, running more than one test at a time can create window-manager-related bugs, and nobody wants to deal with that.

It was actually already the case, I simply added some log about it and unified the code a bit more.

I'm okay reviewing this. I've looked a little bit at the GUI tester and have done some Node before.

Don't hesitate if you have questions then!

@bors r+ rollup

Looks good! One comment on variable naming, which doesn't block merging:

} else if (!no_headless) {

When I see a statement like this I read it as "not no headless", which is a double negative and kind of confusing. Instead you can name the variable headless and invert the sense:

let headless = true;
...
        if (opts["no_headless"]) {
            args.push("--no-headless");
            headless = false;
        }

📌 Commit 1feeda8 has been approved by jsha