Add the stopOnFailure="true" attribute to your phpunit.xml root element.
You can also use it in the CLI: phpunit --stop-on-failure
Info from manual and some others that are maybe useful for you:
- stopOnError – “Stop execution upon first error.”
- stopOnFailure – “Stop execution upon first error or failure.”
- stopOnIncomplete – “Stop execution upon first incomplete test.”
More info at: PHPunit manual