Add bats_teardown_trap to existing EXIT trap instead of overwriting.

Please consider adding to any existing signal traps rather than simply replacing them. There are some examples on StackOverflow of how to do this, such as:

trap_add() {
    trap_add_cmd=$1; shift || fatal "${FUNCNAME} usage error"
    new_cmd=
    for trap_add_name in "$@"; do
        # Grab the currently defined trap commands for this trap
        existing_cmd=`trap -p "${trap_add_name}" |  awk -F"'" '{print $2}'`

        # Define default command
        [ -z "${existing_cmd}" ] && existing_cmd="echo exiting @ `date`"

        # Generate the new command
        new_cmd="${existing_cmd};${trap_add_cmd}"

        # Assign the test
         trap   "${new_cmd}" "${trap_add_name}" || \
                fatal "unable to add to trap ${trap_add_name}"
    done
}

This came up for me because I'm starting a local fake backend for my tests to hit. I start it as a background process, and I want to clean it up when tests are done. Within a single test I can do something like trap_add and setup/teardown my local backend within the test, but it would be great if BATS took care of it.

(In the context of a whole test suite it's actually OK, because I set up my local backend outside of BATS and then tests run as subshells with separate traps.)

sstephenson / bats

Add bats_teardown_trap to existing EXIT trap instead of overwriting. #272