Add expectErrorLog() for expecting error_log() output

[staabm]

summary:

• when a test which invokes error_log() without a call to expectsErrorLog(), the output is directly rendered in-between the summary (as tested in Regression test for error_log() #6127)
• when a test which invokes error_log() with a call to expectsErrorLog(), no more output is rendered in-between the test summary printing. when no error_log() is invoked the test is considered failed.

---

backstory:

while looking into #2155 (comment) I realized PHPunit is already somehow capturing the error_log() output.

I think this means we don't need a workaround like #2155 (comment) in phpunit itself, but just a API which allows us to make assertions on the already captured output.

DX wise I think there is also some room for improvement since the error_log'ged string just shows up in the test-debug output without any indication where this string is coming from (the test-author needs to look into the code beeing tested to realize that this string originates from a error_log) or how to make assertions on it.

With this PR I am just sending a test so we can see the status quo and discuss where to move from here

closes #2155

[staabm]

I tried debugging it a bit more to find out how phpunit knows what the unit-under-test passed to error_log in the PRs test-case.

PHPUnit Started (PHPUnit 12.0-gd39bf28f4 using PHP 8.3.16 (cli) on Darwin)
Test Runner Configured
Bootstrap Finished (/Users/m.staab/Documents/GitHub/phpunit/tests/bootstrap.php)
Event Facade Sealed
Test Suite Loaded (1 test)
Test Runner Started
Test Suite Sorted
Test Runner Execution Started (1 test)
Test Suite Started (PHPUnit\TestFixture\Issue2155\Issue2155Test, 1 test)
Test Preparation Started (PHPUnit\TestFixture\Issue2155\Issue2155Test::testOne)
Test Prepared (PHPUnit\TestFixture\Issue2155\Issue2155Test::testOne)
logged a side effect
Test Passed (PHPUnit\TestFixture\Issue2155\Issue2155Test::testOne)
Test Finished (PHPUnit\TestFixture\Issue2155\Issue2155Test::testOne)
Test Suite Finished (PHPUnit\TestFixture\Issue2155\Issue2155Test, 1 test)
Test Runner Execution Finished
Test Runner Finished
PHPUnit Finished (Shell Exit Code: 0)

I can see the string also be mentioned in the event log stream of --debug.
@localheinz could you give me a hint how I can find out where this logged a side effect string is coming from?

[staabm]

ohh I think I understand the problem now. error_log is just writing into stderr. its not a event happening and beeing rendered by the event system

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.09%. Comparing base (fb459a7) to head (18a89b4).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6118   +/-   ##
=========================================
  Coverage     95.09%   95.09%           
- Complexity     6739     6742    +3     
=========================================
  Files           724      724           
  Lines         21267    21278   +11     
=========================================
+ Hits          20223    20234   +11     
  Misses         1044     1044           

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[staabm]

I think we are in better shape now (put a new summary into the PR description)

[sebastianbergmann]

This should be expectErrorLog() to be consistent with expectOutputString, for example.

[sebastianbergmann]

expectErrorLog() is a new feature. Therefore, we should not put its end-to-end tests into the regression directory. The generic would be acceptable for now.

[staabm]

great catch, fixed it. thank you!