PHP CLI increase memory limit

Sometimes, when you are running a PHP script from command line interface(CLI), a higher memory limit may be required in order for the script to be successfully executed.
This can be done by using the "-d" or "–define" option in the command. 

php -d memory_limit=2048m bin/phpunit

In my case, I want to run a project's tests that have high memory consumption.

Here is the link to the php manual's command line features and also directly for the command line options