tests: make inverted tests actually count

"! test ..." does not cause the script to fail, even with set -e.
IIUC, bash treats this command as part of an expression line, as it
would if 'test ... && ...' was used. Failing expression lines do not
terminate the script.

This fixes the obvious cases by changing '! test' → 'test !'.
Then the inversion happens internally in test and bash will propagate
the failure.