I am a wireframe engineer and I have been on upwork since last 2 years. I have come accross a lot of jobs where the posters asks "Upworks tests passed in this skillset" and unfortunately there are no such tests.
I had emailed "Balsamiq" a famous wireframeing tool to contact Upwork to post job but I don't think there a mechanism to do that, instead they replies me to contact Upwork on their behalf to create a test for Balsamiq.
I hope this request delivers to you and we can work on creating a test for Balsamiq.
Looking forward to your reply,
Thank you for sharing your feedback and the effort you put into following up on this test. I'll forward the information you provided to our team so they can take a closer look.