/usr/share/gap/pkg/io/tst/sendstringbackground.tst is in gap-io 4.5.1+ds-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | gap> f := IO_File("/dev/null", "w");;
gap> IsBound(HPCGAP) or ForAll([1..3000], x -> IO_SendStringBackground(f, "cheese"));
true
gap> IO_Close(f);
true
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