PHPUnit 10 Assertion failure results in "Uncaught Error: Class "PHPUnit\Framework\TestFailure" not found"

[mnocon]

Hi!

When a PHPUnit assertion fails in a Behat Context class the tests fail with:

~/Desktop/repos/behat-phpunit10 on main !2 ?2 ❯ vendor/bin/behat                                                                                                                                                       14.17.0 at 10:36:00
Feature: PHPUnit 10 exception

  Scenario: Trigger PHPUnitExceptionStringer # features/Reproducer.feature:3
    Given ExceptionStringer is triggered     # FeatureContext::triggerExceptionStringer()
PHP Fatal error:  Uncaught Error: Class "PHPUnit\Framework\TestFailure" not found in /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Testwork/Exception/Stringer/PHPUnitExceptionStringer.php:49
Stack trace:
#0 /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Testwork/Exception/ExceptionPresenter.php(93): Behat\Testwork\Exception\Stringer\PHPUnitExceptionStringer->stringException(Object(PHPUnit\Framework\ExpectationFailedException), 1)
#1 /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Behat/Output/Node/Printer/Pretty/PrettyStepPrinter.php(174): Behat\Testwork\Exception\ExceptionPresenter->presentException(Object(PHPUnit\Framework\ExpectationFailedException))
#2 /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Behat/Output/Node/Printer/Pretty/PrettyStepPrinter.php(95): Behat\Behat\Output\Node\Printer\Pretty\PrettyStepPrinter->printException(Object(Behat\Testwork\Output\Printer\StreamOutputPrinter), Object(Behat\Behat\Tester\Result\ExecutedStepResult))
#3 /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Behat/Output/Node/EventListener/AST/StepListener.php(119): Behat\Behat\Output\Node\Printer\Pretty\PrettyStepPrinter->printStep(Object(Behat\Testwork\Output\NodeEventListeningFormatter), Object(Behat\Gherkin\Node\ScenarioNode), Object(Behat\Gherkin\Node\StepNode), Object(Behat\Behat\Tester\Result\ExecutedStepResult))
#4 /Users/mareknocon/Desktop/repos/behat-phpunit10/behat/src/Behat/Behat/Output/Node/EventListener/AST/StepListener.php(65): Behat\Behat\Output\Node\EventListener\AST\StepListener->printStepOnAfterEvent(Object(Behat\Testwork\Output\NodeEventListeningFormatter), Object(Behat\Behat\EventDispatcher\Event\AfterStepTested))

stopping the test execution.

I've created a reproducer for this issue, if you'd like to test it yourself:
https://github.com/mnocon/behat-phpunit10

PHPunit 9 used the TestFailure class to stringify an Exception:
https://github.com/sebastianbergmann/phpunit/blob/9.6/src/Framework/Exception/Exception.php#L58-L67

but in PHPUnit 10 ThrowableToStringMapper is responsible for that:
https://github.com/sebastianbergmann/phpunit/blob/10.0/src/Framework/Exception/Exception.php#L57-L69
(and the TestFailure class is gone).

I made an attempt at solving this, in #1422

[uuf6429]

Hey, I saw the merged PR and I have a few follow up questions:

1. since it has been merged, shouldn't this ticket be closed (if the problem is now solved)?
2. looking at the code of the PR, I disagree a bit on how it works:
   1. In my understanding, PHPUnitExceptionStringer->supportsException should have prevented the original problem from happening, so I would recommend looking into why it wasn't
   2. The code of PHPUnitExceptionStringer->stringException is now a bit messier.. "if class exists return x; if class does not exist return z; else it must exist and therefore return y..", IMHO this would be clearer and more readable:

   switch (true) {
       case class_exists('PHPUnit\\Util\\ThrowableToStringMapper'):
           return trim(\PHPUnit\Util\ThrowableToStringMapper::map($exception));
   
       case class_exists('PHPUnit\\Framework\\TestFailure'):
           // PHPUnit assertion exceptions do not include expected / observed info in their
           // messages, but expect the test listeners to format that info like the following
           // (see e.g. PHPUnit_TextUI_ResultPrinter::printDefectTrace)
           return trim(\PHPUnit\Framework\TestFailure::exceptionToString($exception));
   
       case class_exists('PHPUnit_Framework_TestFailure'):
           return trim(\PHPUnit_Framework_TestFailure::exceptionToString($exception));
   
       default:
           // TODO this should also be somehow handled
   }

   It now also exposes the original flaw, which the patch didn't fix adequately IMO.
3. Shouldn't PHPUnitExceptionStringer->supportsException also be updated to handle the new formatter?