Between latest Canary 2.0.6.106 and the test build (i.e. as requested).
FTP (Alternative) introduced a more ambitious test. In a way it’s better.
There are, though, more things that could go wrong, due to complexity.
Typically the test is TestList which does a list. Exact listing is ignored.
AlternativeFTP tests permissions too by doing a put, get, and delete.
Issue 1 is just have no pre-existing folder of that name. Test connection.
Issue 2 depends on FTP server, but on Windows I finally used the folder
Right-click → Properties → Security → Advanced to make permissions
explicit rather than inherited from C:\ and took away all write permission.
As Test connection tries to test permissions, that should be noticed…