For constructing test scripts, use std::vector and, in particular, std::vector::insert to insert 20 zero bytes rather than listing the full array of bytes explicitly. This makes the code easier to read and makes it immediately obvious what the structure of the data is, without having to count the zeros to understand it.
Of course, that is a matter of taste - so if you disagree that the change makes the code easier to read, let me know.
This has been split out of #14752.