[random test failure] ConnectionUnitTest::testOpenQueryClose

Problem/Motivation

Drupal\Tests\mysql\Kernel\mysql\ConnectionUnitTest::testOpenSelectQueryClose
Failed asserting that an array does not have the key 907.

core/tests/Drupal/KernelTests/Core/Database/DriverSpecificConnectionUnitTestBase.php:98
core/tests/Drupal/KernelTests/Core/Database/DriverSpecificConnectionUnitTestBase.php:178

Steps to reproduce

Proposed resolution

Instead of waiting 20ms for the connection to close, introduce a waitFor function that will test every 10ms if the connection is closed, timing out after 100ms.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet