readonly a=A
b=B
readonly b
# readonly on already readonly var is harmless
readonly b a
readonly | grep '^readonly [ab]='
# this should work
export a b
export -n a b
echo Ok:$?
env | grep -e^a= -e^b=  # shows nothing

# these should all fail (despite the same value being assigned)
# bash does not abort even in non-interactive more (in script)
true
a=A
echo Fail:$?; true
readonly a=A
echo Fail:$?; true
export a=A
echo Fail:$?; true
a=A echo Visible:$? # command still runs
unset a
echo Fail:$?; true