Add PHPUnit missing in dependencies

[lbajsarowicz]

Description

Basically in composer.json there's a PHPUnit dependency missing, so that bin/phpunit-checks is unable to run if phpunit is not installed globally.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/verification tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests

[okolesnyk]

@lbajsarowicz composer.lock should be updated also.

[coveralls]

Coverage increased (+0.008%) to 57.411% when pulling d24ac0a on M2Coach:missing-phpunit into a9e04a7 on magento:develop.

[coveralls]

Coverage remained the same at 57.392% when pulling 5a4e2ef on M2Coach:missing-phpunit into 7136da4 on magento:develop.

[lbajsarowicz]

@okolesnyk composer.lock commited.

[lbajsarowicz]

@aljcalandra just want to stay compliant with Magento 2 core. Is there any reason to introduce dependency that does not stay in line with core?

[okolesnyk]

@lbajsarowicz
MFTF can also be used as a Stand-alone tool, so we think it is ok first of all to support what Magento supports and adding an additional possible version of PHPUnit. Also we do this for possible future updates of PHPUnit dependency in Magento.

[lbajsarowicz]

@okolesnyk As far as I see you still want to have compatibility with PHP 7.0, but

I ran composer update from PHP 7.0 to keep composer.lock compliant with PHP 7.0, so it has not changed (that's why it was not commited)

[okolesnyk]

@lbajsarowicz
Yes you are right that we want to keep PHP 7.0 because we work with Magento 2.2 which supports this version as you can see https://github.com/magento/magento2ce/blob/2.2-develop/composer.json#L11

And thank you for this PR, it is really make sense to specify PhpUnit dependency.
If you have a second please fetch latest develop and resolve conflicts, if not we'll take care of it ones we ready to merge it.

Thank you!

[lbajsarowicz]

@okolesnyk Ready.