WopiTestFrame does not work - WOPI host implementation

According to the documentation, the Office Online Server 2016 includes a WOPI Validation application:

http://wopi.readthedocs.io/en/latest/build_test_ship/validator.html

Note that the server itself works fine (one can view and edit documents - no issue). Just this "WOPI Test" thing is not there. Did anybody really tried to call test page - means, does this bloody test page really work at all for anybody at all?! Google search gives 6 pages, 3 of them refer to the above link, 3 other to some garbage :)

My problem is, if you follow the documentation, you always hit error "We're sorry. An error has occurred. We've logged the error for the server administrator."

The thing is, this error is not really logged anywhere (ULS logs and event logs are virgin clean).

The real reason for that appears to be that the page itself ("WopiTestFrame.aspx") is just not there. How do I make it to be there?

The page is listed in the /hosting/discovery as available:

The WopiTestFrame.aspx is only present in Office Online - the on-demand version of Office with which you can integrate if you are a member of the Office 365 - Cloud Storage Partner Program.

Though most of the documentation at https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/ is common with Office Online Server 2016, it was mainly written for the purposes of the aforementioned integration.