A script that generate a repository with random commits and one bug (return code) in one of them

generate_bisect_repo.sh

#!/bin/sh

mkdir git-bisect-test
cd git-bisect-test
git init

echo "#!bin/sh\n" > script.sh
echo "exit 0" >> script.sh
git add script.sh
git commit -a -m "initial commit"

COUNTER=0
COMMITS_COUNT=$(($RANDOM % 100))
BUG_INDEX=$(($RANDOM % $COMMITS_COUNT))
while [  $COUNTER -lt $COMMITS_COUNT ]; do
    if [ $COUNTER = $BUG_INDEX ]; then
        echo "#!/bin/sh\n" > script.sh
        echo "exit 3" >> script.sh
    else
        echo "#" >> script.sh
    fi

    let COUNTER=COUNTER+1 
    git commit -a -m 'dunno'
done

FIRST_PARENT=`git rev-list HEAD | tail -n 1`

echo "\n"
echo "START BISECT WITH 'git bisect start HEAD $FIRST_PARENT'\n"
echo "THEN START AUTOMATE TEST 'git bisect run sh script.sh'\n"
echo "OR USE AN EXTERNAL SCRIPT FILE 'git bisect run ../test.sh'"