running a phpUnit test within a docker container
Don't quote the command you're trying to run, just do:

docker run --rm -it -v ~/Users/mow/Documents/devFolder/testdev:/app testdev_php php ./vendor/bin/phpunit


Your image is looking for a file called "php ./vendor/bin/phpunit" instead of looking for "php" and passing everything else on the line to it. 

This is the real reason docker requires all your parameters before the image, because the parameter after the image is the command and everything after it is parameters to that command - don't quote everything. 

The Dockerfile equivalent is:

ENTRYPOINT ["/init","parameter1","parameter2","parameter3"]


If it still doesn't work, check the parent Dockerfiles for the location of "php" 

docker run --rm -it -v ~/Users/mow/Documents/devFolder/testdev:/app testdev_php /usr/local/bin/php ./vendor/bin/phpunit