Reproduction steps:
1. Open the attached project "ReproProj"
2. Open the Test Runner (Window > General > Test Runner)
3. Select "Player" at the top (rightmost of the three buttons)
4. Click “Run All“
5. Wait for the Player window to open and close
6. Observe Test Runner

Expected result: Test Runner shows either that the tests passed or failed
Actual result: Test Runner tests show neither the green checkmark nor the red "failed" icons

Reproducible with: 6000.0.54f1, 6000.1.14f1, 6000.2.0b12, 6000.3.0a3
Could not test with: 2022.3.62f1 (Packages\de.codesmile.packagetest\Tests\NewTestScript.cs(17,6): error CS0246: The type or namespace name 'UnityTestAttribute' could not be found)

Reproducible on:
Player

Not reproducible on:
Play Mode
Edit Mode

Testing environment: Windows 10 Enterprise 21H2
Not reproducible on: No other environment tested

Notes:
- Renaming the test's Assembly Definition Name property in the Inspector so that it does NOT start with "UnityEngine.CoreModule" (i.e., add a prefix) will make the tests run
- The tests will also run despite the "UnityEngine.CoreModule" name when Player Settings / Managed Stripping Level is set to "None", but will fail even for "Minimal" code stripping
- The test will also run despite the "UnityEngine.CoreModule" name if the Test folder is moved from the package to “/Assets”