This fix implements a custom serialize/deserialize method on the ComparisionFailure class, which means it loses the stack trace during serialization.

This allows PHPUnit to run in process isolation mode when the stack trace may contain references to non-serializable objects such as the PDO.

Codecov Report

Merging #47 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #47      +/-   ##
============================================
+ Coverage     99.07%   99.09%   +0.02%     
- Complexity      123      125       +2     
============================================
  Files            15       15              
  Lines           325      333       +8     
============================================
+ Hits            322      330       +8     
  Misses            3        3

Impacted Files	Coverage Δ	Complexity Δ
src/ComparisonFailure.php	100% <100%> (ø)	11 <2> (+2)	:arrow_up:

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@sebastianbergmann I've re based on the current master branch. Is there any chance of getting this merged?

Also I think the codecov-io report is for the previous version against the current master; rather than the current version of this PR

@DomBlack The problem still exists so I wrote the patch: mpyw/phpunit-patch-serializable-comparison

@sebastianbergmann @DomBlack We've been running into this issue in the Drupal community as well. I see this PR does need an update to use the __serialize and __unserialize magic methods introduced in php 7.4, rather than implementing the Serializable interface. If we can get an updated PR, I'd like to know the chances of being able to get it merged, as we could definitely use it downstream.

Related Drupal Core issue: https://www.drupal.org/project/drupal/issues/3197324

The only thing I can promise that I would review such a pull request.

I am running into similar issue as well with having object as args on the stack trace that cannot be serialized when running in isolation.

Which is related to issue: sebastianbergmann/phpunit/issues/1351 and pull: sebastianbergmann/phpunit/issues/1352

In that PR, instead of trying to override serialization methods, the constructor just unset the args on each stack element: see commit for Framework/Exception.php

Relevant code from Framework/Exception.php in that PR:

    public function __construct($message = '', $code = 0, Exception $previous = null)
    {
        parent::__construct($message, $code, $previous);

        $this->serializableTrace = $this->getTrace();
        foreach ($this->serializableTrace as $i => $call) {
            unset($this->serializableTrace[$i]['args']);
        }
    }

maybe a similar approach could be utilized in ComparisonFailure?

-- edit/update to my own message... After digging into this one a bit more, seems that overriding the serialization methods probably is the best route, just leaving my original comment for additional information.

Added a (very naive) first stab at updating the old PR in #106.