use printf instead of echo in testing framework

use printf instead of echo in testing framework

The behaviour of echo "\tA\t" differs between dash/zsh which interprets
the \t as tab and bash which prints it literally. Similar things happen
for other escape sequences – without the -e flag.
Switching to printf makes this more painless^Wportable, so that the
tests are also working correctly with bash as sh.
(commit message by committer, patch otherwise unmodified)