this regression test reproduces erlang/rebar3#2558
the test will succeed when #906 is applied and fail otherwise
while there make shelltest/run_test.sh also work on platforms where sed(1) is of the BSD/MacOS variant (BSD/MacOS sed does not work with a bare -i flag and GNU sed does not work with -i '' so using a backup for the in-place edit and remove it afterwards is the least painful solution that works for both)
shelltest/run_test.shalso work on platforms wheresed(1)is of the BSD/MacOS variant (BSD/MacOS sed does not work with a bare-iflag and GNU sed does not work with-i ''so using a backup for the in-place edit and remove it afterwards is the least painful solution that works for both)