Does not work on PHPUnit 8

[Bilge]

This library makes the (wrong) assumption that we should not want to use it (even though we installed it for some reason) on PHPUnit 8, with its custom autoloader that makes the ArraySubsetAsserts trait do nothing. In that case, PHPUnit 8's implementation will run as normal and issue a deprecation warning, which will also cause the tests to fail if failOnWarning="true" is being used in the PHPUnit config. I should think that if this library is installed, it's a fair bet we want to use it.

[jrfnl]

This library - in its current state - is a polyfill, which means that it will only kick in when the functionality is not available natively in PHPUnit.

As of the latest release, you can safely require-dev this library in combination with PHPUnit 8 (and older), making it easier for this library to be used in projects which need to run tests in a variety of PHPUnit versions, including PHPUnit 9 (in which the functionality was removed).
And yes, in case PHPUnit < 9 is detected, it will fall back to the PHPUnit native functionality, which means that in PHPUnit 8, the deprecation warning will show.

To change that, the code in the actual polyfill would need to be made compatible with PHP < 7.3, which the maintainer of this library has indicated is not desired.

[Bilge]

I don't really understand why 7 and 8 suddenly need to share the same code when it's clear that, for example, 8 and 9 do not currently.

[jrfnl]

@Bilge I'm not sure I understand your remark. Prior to the last release, this library couldn't even be installed in combination with PHPUnit 8.

[joshua-bn]

We don't want the warnings is the point. In 8 we get warnings. We understand that it is deprecated - that's why we installed this.

[marcosh]

Happened to me, too. I installed this library to get rid of the warnings in PHPUnit8 but I still got them. It would be nice to have the chance to choose to use the library code instead of the one provided by PHPUnit

EDIT: I hacked my way through it by overriding the autoload and just using PSR-4

[jrfnl]

PR #65 should address this. Testing appreciated.