I installed MySQL via MacPorts. What is the command I need to stop the server (I need to test how my application behave when MySQL is dead)?
There are different cases depending on whether you installed MySQL with the official binary installer, using MacPorts, or using Homebrew:
brew services start mysql
brew services stop mysql
brew services restart mysql
sudo port load mysql57-server
sudo port unload mysql57-server
Note: this is persistent after a reboot.
sudo /Library/StartupItems/MySQLCOM/MySQLCOM stop
sudo /Library/StartupItems/MySQLCOM/MySQLCOM start
sudo /Library/StartupItems/MySQLCOM/MySQLCOM restart