Ubuntu's ln -f dies if you do "ln -s link link; ln -sf / link". Toybox's
ln -f does the rm and retry if the first attempt fails for any reason.
So if you run the readlink test with an ubuntu host $PATH, it fails, but
it works with a toybox host path.
diff --git a/tests/readlink.test b/tests/readlink.test
index bb25985..48104e5 100755
--- a/tests/readlink.test
+++ b/tests/readlink.test
@@ -48,6 +48,7 @@
"$APWD/sub/boing\n" "" ""
testing "-f /dev/null/file" \
"readlink -f /dev/null/file 2>/dev/null || echo yes" "yes\n" "" ""
+rm link
ln -sf / link || exit 1
testing "-f link->/" "readlink -e link/dev" "/dev\n" "" ""
testing "-f /dev/null/.." \
