What do you think about adding a force="true" parameter instead as we can do when setting APP_ENV for instance.
I don't actually know how this works but it would probably look more explicit.

4.4 might benefit from that too isn't it?
Meanwhile, you can (and propably should) set COMPOSER_NO_INTERACTION=1 in CI jobs.

@nicolas-grekas the SYMFONY_PHPUNIT_REQUIRE was introduced in 5.3 and so not part of 4.4.

@yoannrenard the force parameter has another meaning in the phpunit xml this forces the env if a real env is set.

Another way I thought to remove the whole require-dev part of the installed phpunit version. Then also the composer require would not throw any warning, and so phpunit dev dependencies would not have any effects.

Thank you @alexander-schranz.