You can create as many subpages under your user namespace as needed. For example, User:Traveler/Test is acceptable.
Topic on User talk:Traveler
Please use subpages rather than make a new account
Understood. Is there any way to create a hidden/password-protected/unlisted subpage?
I haven't heard about anything like it. Pages can be protected and then specified users-groups will be allowed to edit them while others will be not, but I don't think it's possible to restrict editing for everyone but certain user.
Making more accounts won't help with that because all pages work the same. Even if your account is protected by password, pages you create or contribute to are not.
Asking admin to protect your page from non-confirmed users (people who don't have wiki account) is one way to prevent unwanted edits.
Another one would be to make editing the content you want to protect harder. As an example, you can't edit my sample teams by editing my main userpage, I can't either for that matter, and it's because the actual content is on another page and sections of that page are then transcluded to my main in order I want them to be shown. You can access said page by clicking one of the images but that's just for my convenience. Without posting the link to said page anywhere or making it easily accessible otherwise, I could lower the possibility of someone going there and messing up my stuff.
When you say create a draft/test page, do you mean orphan test pages?