Minimal code example for https://stackoverflow.com/questions/64232453/bats-how-to-force-a-check-for-existence-of-a-program-to-fail

ds.sh

#!/usr/bin/env bash

ds() {

    is_command() {
      [[ -x "$("${command}" -v "$1" 2> /dev/null)" ]] && return 0
      return 1
    }

    is_command 'dos2unix' || { echo 'dos2unix is required'; exit 1; }

    exit 0;
}

test.bats

#!/usr/bin/env bats

source "${BATS_TEST_DIRNAME}/ds.sh"

@test 'dos2unix does not exist' {
    hash -r

    BASH_CMDS['dos2unix']='/no/such/dir/dos2unix'

    run ds

    [ "${status}" -eq 1 ]
    [ "${output}" = 'dos2unix is required' ]
}