$bookseller = Koha::Acquisition::Bookseller->fetch({ id => $booksellerid });
# Ensure that the preference 'LetterLog' is set to logging
-C4::Context->set_preference( 'LetterLog', 'on' );
+t::lib::Mocks::mock_preference( 'LetterLog', 'on' );
{
warning_is {