To reproduce:
composer install
vendor/bin/phpunit tests/BarTest.php
vendor/bin/phpunit tests/FooTest.php
Output of vendor/bin/phpunit tests/BarTest.php:
PHPUnit 9.1.4 by Sebastian Bergmann and contributors.
. 1 / 1 (100%)
Time: 00:00.024, Memory: 4.00 MB
OK (1 test, 1 assertion)
Output of vendor/bin/phpunit tests/FooTest.php:
PHPUnit 9.1.4 by Sebastian Bergmann and contributors.
W 1 / 1 (100%)
Time: 00:00.026, Memory: 6.00 MB
There was 1 warning:
1) Warning
No tests found in class "App\Tests\ParentFooTest".
WARNINGS!
Tests: 1, Assertions: 0, Warnings: 1.