When entering into debugger (byebug) with guard-minitest, I am unable to see the output while I am typing. I have seen this problem with Rails 4.2.8 as well as Rails 5.
If I run the test outside of guard, the debugger works fine.
byebug (9.0.6)
guard (2.14.1)
guard-minitest (2.4.6)
rails (4.2.8)
do you have rb-readline
gem installed?
In my case removing it from Gemfile
solved this issue!