Upgrade PHPUnit version

[raaaahman]

Update

Since the release of PHP 8, it is not possible to use a single PHPUnit version to test with PHP versions from 5.6 to 8.

We could draw inspiration from:

• WordPress/wordpress-develop: The WordPress Core team has adapted PHPUnit 7.5 to not break with PHP8.
• woocommerce/woocommerce: Uses quite the same trick, but goes further into creating its own fork of PHPUnit 7.5
• Yoast/wordpress-seo: Created a composer package to use different versions of PHPUnit given the PHP version tested.

Changes

• Update the version of PHPUnit to 7.5.20.
• Integrates JohnKary's Speedtrap Listener instead of a custom one.

Going further

• Actually, the versions of PHPUnit we can use is limited to 7.x as long as WordPress needs to support PHP 5.6. There is an ongoing discussion about WordPress support for PHP on Trac.
• To test with another PHP version than your current one, you can use the experimental-docker branch (but you will need to merge or cherry-pick this branch into your current working branch, remember to make a copy of it). See more info in Docker container to check compatibility with PHP versions #18

Fixes #12

[jonathanbossenger]

@raaaahman I'm going to leave this open until we make a call on #18, as that decision might affect this one.

[raaaahman]

@raaaahman I'm going to leave this open until we make a call on #18, as that decision might affect this one.

I don't think so. The tests can run on local environment as well (they couldn't before).

[jonathanbossenger]

I don't think so. The tests can run on local environment as well (they couldn't before).

Aha, ok thanks. I will do my best to test this out in the coming week.