There are actually 3 issues

1. When pressing test button on SSH item, the get value from host is grayed out - it is not possible to specify different host

It is not possible to specify host at all if testing from template

2. When using plain text user name / password on SSH agent item, everything works

When using User macros in username / password fields, test fails 

After fixing macros, please check that protected User Macros are also working
 
3. It is not possible to change macro values from test screen