Writing applications with QuickFIX has some fun. The FIX engine there is a classical IoC, event driven. Application that uses it has to have only business specific things don't bother with tedious FIX noodles. Easy peeasy.
However, sometimes I have had anxiety because that specifics were not covered properly by tests. No, I tried, tried hard really. With mock or without it, tests for application with QuickFIX looks ugly and non readable due its restrictive and cumbersome design. Very often I had to remove them or simplify their verification because clearly understood that after couple months even I will not be able support it.
Eventually I came to an idea to simplify all that. QuickFIX users may appreciate this. :)