Copy the script below for adding the testbranch function to your .zshrc file.
# With curl:
bash <(curl -sL https://gist.githubusercontent.com/jagoncalves14/849e38b98d8e3e80a59d43a1504da58e/raw/5c75984310095d5b8c31c883d6909dc53a17891d/add-testbranch-to-zsh.sh)
# With wget:
bash <(wget -nv -O - https://gist.githubusercontent.com/jagoncalves14/849e38b98d8e3e80a59d43a1504da58e/raw/5c75984310095d5b8c31c883d6909dc53a17891d/add-testbranch-to-zsh.sh)