Mocking \ReflectionClass throws an error in PHPUnit 8.5 when run with PHP>=8.1

[m-vo]

Q	A
PHPUnit version	8.5
PHP version	8.1
Installation Method	Composer

Summary

Mocking \ReflectionClass throws an error in PHPUnit 8.5 when run with PHP>=8.1.

Current behavior

Throws an exception: Call to undefined method ReflectionUnionType::getName().

How to reproduce

// Execute with PHP>=8.1
$this->createMock(\ReflectionClass::class);

Expected behavior

Works like in PHPUnit 9.3.

[sebastianbergmann]

Life Support means that changes will be made for an otherwise unsupported version of PHPUnit to be compatible with new versions of PHP. Life Support ends when an old version of PHPUnit cannot be made compatible with a new version of PHP without breaking backwards compatibility.

The fact that a version of PHPUnit supports a specific PHP version means that this version of PHPUnit works on that PHP version for PHP code that is compatible with the version of PHP required by the PHPUnit version in question. For example, PHPUnit 8.5 requires PHP 7.2. PHPUnit 8.5 works for PHP code compatible with PHP 7.2 on PHP 8. However, PHPUnit 8.5's test double code generator does not support PHP 8's union types syntax, for example.

[sebastianbergmann]

While it is not a good idea to double classes such as ReflectionClass, this should probably be fixed. However, adapting PHPUnit 8.5 for arcane use cases such as this to changes in PHP 8.1 is not very high on my list of priorities. I will, of course, gladly consider a pull request that addresses this.

[wilsonge]

@sebastianbergmann happy to do the pull request (we're needing to support this same thing for some failing php 8.1 unit tests in @joomla - due to some slightly suspect mocks we're doing of XMLReader on our end) - done a first part to the type repo at sebastianbergmann/type#24 and then can pick that up in this repo as a part two if accepted.

[sebastianbergmann]

I have explained in sebastianbergmann/type#24 (comment) why support for union types and intersection types will not be backported to PHPUnit 8.5.

If this issue cannot be fixed without a backport of union types and intersection types then this issue will not be fixed. Internal classes such as ReflectionClass or XMLReader should not be doubled anyway.