./Executable < test1.in > mytest1.out

for f in test*.in; do ./tetris <"$f" >"my${f%in}svg"; done

diff mytest1.out test1.out > difftest1.txt

for f in mytest*.svg; do diff "$f" "###what goes here?###" > "diff${f%in}txt"; done

for i in {1..2}; do
    diff test${i}.out mytest${i}.out &>/dev/null
    es=$?
    if [ $es -ne 0 ]; then
        echo "difference found"
    else
        echo "success"
    fi
done

difference found
success

diff test${i}.out mytest${i}.out > difftest${i}.txt

  if ! [[ -s difftest${i} ]]; then
      echo success
  else
      echo "difference found"
  fi