Because of [https://community.devsense.com/d/2483-projectsystempackage-did-not-load-correctly/33] I updated to VS 2026.

The Problem with not loading the extension correctly seems gone, but there is another issue with Test-Explorer.

The tests are executed successfully and Visual Studio knows the final run result, but the Test Explorer does not update the status of the individual tests/groups correctly.

For example, after running 24 tests, the Test Explorer shows:
Test run completed: 24 Tests (24 successful, 0 failed, 0 skipped)
However, the corresponding test group still remains in the blue/unknown state instead of being marked green/successful.

So the issue is not that PHPUnit fails to produce a result. The overall result is available, but the individual test results are not correctly applied/displayed in the Test Explorer tree.

Test-Output generates an error message:
Fehler beim Hinzufügen des Ergebnisses für den Test ... = Error adding the result for the test ...

Test-Output (for 1 single test):

Erstellen von Test Projekten
========== Testlauf wird gestartet ==========
Running test configuration ...
Config: 'R:\mypath\phpunit.xml'
Path: 'R:\mypath'
Filter: --filter "(^(AquariHelpTest::test_00100_Basic_DB_Connect_00100(\s.*)?)$)i"
>> "C:\Program Files\IIS Express\PHP\v8.5\php.exe" -ddisplay_errors=1 "-cC:\Program Files\IIS Express\PHP\v8.5" "R:\mypath\vendor\bin\phpunit" -c "R:\mypath\phpunit.xml.tmp" --teamcity --colors=never --testsuite PhpTools_TestSuite --filter "(^(AquariHelpTest::test_00100_Basic_DB_Connect_00100(\s.*)?)$)i"
PHPUnit 13.3.1 by Sebastian Bergmann and contributors.
Runtime:       PHP 8.5.4
Configuration: R:\mypath\phpunit.xml.tmp
Fehler beim Hinzufügen des Ergebnisses für den Test "r:\mypath\phpunit.xml..00100basicdbconnect00100" mit der ID "209f6d5c-33ce-587b-975a-450f14217e58".
Time: 00:03.561, Memory: 22.00 MB
OK, but there were issues!
Tests: 1, Assertions: 1, Warnings: 1, Deprecations: 2, PHPUnit Deprecations: 1.
========== Testlauf beendet: 1 Tests (1 erfolgreich, 0 fehlerhaft, 0 übersprungen) in 7 Sek. ausgeführt ==========

If I install PHP Tools 1.84 in VS 2026, the Testsresults are displayed correctly. After updating to 1.90.19154 the problem occures (tried also with 19.157, same problem).
I'm currently using phpunit 13.3.1, but I also tried 10.5.x and 12.5.x.

Thank you in advance for your help.

Stefan