Invalid & convoluted Bash scripting fixed

cumbersome.sh

#!/usr/bin/env bash

set -Eeuo pipefail

function testing.of() {
  local what
  what="${1:?Pass what as arg[1]}"
  echo "Testing of ${what}..."

  eval "non-existing-showcase-command ${what}"
}

function do.aaa() {
  echo 'Doing Aaa...'
  
  if echo "${SCOPE:-}" | grep -q aaa; then
    testing.of aaa || return $?
  fi

  echo 'Done Aaa.'
}

function do.bbb() {
  echo 'Doing Bbb...'
  
  if echo "${SCOPE:-}" | grep -q bbb; then
    testing.of bbb || return $?
  fi

  echo 'Done Bbb.'
}

failed=0

(( !failed )) && do.aaa || failed=1
(( !failed )) && do.bbb || failed=2

(( failed )) && exit $failed

echo 'SUCCESS!'

invalid.sh

#!/usr/bin/env bash

set -Eeuo pipefail

function testing.of() {
  local what
  what="${1:?Pass what as arg[1]}"
  echo "Testing of ${what}..."

  eval "non-existing-showcase-command ${what}"
}

function do.aaa() {
  echo 'Doing Aaa...'
  
  if echo "${SCOPE:-}" | grep -q aaa; then
    testing.of aaa
  fi

  echo 'Done Aaa.'
}

function do.bbb() {
  echo 'Doing Bbb...'
  
  if echo "${SCOPE:-}" | grep -q bbb; then
    testing.of bbb
  fi

  echo 'Done Bbb.'
}

failed=0

(( !failed )) && do.aaa || failed=1
(( !failed )) && do.bbb || failed=2

(( failed )) && exit $failed

echo 'SUCCESS!'

proper.sh

#!/usr/bin/env bash

set -Eeuo pipefail

function stacktrace() {
  local code="${1:-$?}"
  set +o xtrace
  echo -e "\n\033[1;31mFAIL! Exiting with status ${code}!\033[0m\n"
  if [ ${#FUNCNAME[@]} -gt 2 ]
  then
    echo "Call tree:"
    echo " 0: ${BASH_SOURCE[1]}:${BASH_LINENO[0]} ${BASH_COMMAND}"
    for ((i=1;i<${#FUNCNAME[@]}-1;i++))
    do
      echo " $i: ${BASH_SOURCE[$i+1]}:${BASH_LINENO[$i]} ${FUNCNAME[$i]}(...)"
    done
  fi
  exit "${code}"
}

trap stacktrace ERR

function testing.of() {
  local what
  what="${1:?Pass what as arg[1]}"
  echo "Testing of ${what}..."

  eval "non-existing-showcase-command ${what}"
}

function do.aaa() {
  echo 'Doing Aaa...'

  if echo "${SCOPE:-}" | grep -q aaa; then
    testing.of aaa
  fi

  echo 'Done Aaa.'
}

function do.bbb() {
  echo 'Doing Bbb...'

  if echo "${SCOPE:-}" | grep -q bbb; then
    testing.of bbb
  fi

  echo 'Done Bbb.'
}

do.aaa
do.bbb

echo 'SUCCESS!'