MS SQL 2014 AlwaysOn High Availibiliity, Error 15023, not about to connect on failover
It's likely that your Test-User account has different SIDS on the primary and replica servers.  The best way to resolve this is drop the Test User on the Secondary, generate a create user statement from the primary with the proper SID (e.g. sp_revlogin, dbatools.io, or another tool of your choice) and then run that generated CREATE USER statment against the secondary.  This will create a user that has the same SID on both replicas so you won't get this error going forward.

Another option, and one that I would recommend instead, is to convert this database to a Partially Contained Database so that all SQL Logins you create with the database are automatically transferred over to any replicas you setup.  This is a very handy feature (if the limitations don't adversely affect you) for databases in Availability Groups and will help minimize the administrations headaches that come with them.