Revert "Remove newly added test for open with :ra mode"
Revert "Remove newly added test for open with :ra mode"

This reverts commit 418466f8bc0d5dc304d1ad0541a8a688c3ad3a1f.

cmp. https://irclog.perlgeek.de/perl6-dev/2017-04-13#i_14424307

dogbert17/roast,bitrauser/roast,dogbert17/roast,bitrauser/roast,perl6/roast