If configured with --disable-cryptsetup (e.g. if only veritysetup is
required), these tests won't be able to run cryptsetup, so they need
to be skipped.
AFAIK older versions of the POSIX Standard didn't specify a way to
locate commands. Many operating systems and distributions added a
which(1) utility for that purpose, unfortunately without consistent
behavior across the board.
OTOH POSIX.1-2008 (or was it older? POSIX.1-2001 mentions it too, but
with a restriction: “On systems supporting the User Portability Utilities
option”) specifies that `command -v` can be used for that purpose:
https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/utilities/command.html
Moreover the standard adds that if the argument is neither a valid
utility, builtin, shell function nor alias then “no output shall be
written and the exit status shall reflect that the name was not found”.
It's therefore no longer needed to void the error output (spewing error
messages was one of the inconsistent behavior of the different which(1)
utilities).
The upcoming Debian 12 (codename Bookworm) appears to have deprecated
its which(1) utility (as a first step for its removal from the base
system):
$ which foo
/usr/bin/which: this version of `which' is deprecated; use `command -v' in scripts instead.
In most places the deprecation notice isn't visible when running the
test suite because most `which` calls run with the error output
redirected to /dev/null, however this is not the case everywhere:
https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.4.3/tests/integrity-compat-test#L333https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.4.3/tests/reencryption-compat-test2#L232
This commit replaces all `which` calls from tests/* with `command -v`,
and removes the error output redirection.
