Issue #3075608 by mondrake, Mile23, longwave: Introduce TestRun objects and refactor TestDatabase to be testable

Issue #3266568 by mxr576, sourabhjain, quietone: Refactor array_merge() usage in loops as possible for performance

Issue #3293446 by alexpott, daffie: Create less static cache in ExtensionDiscovery during KernelTests

Issue #3298906 by andypost, alexpott: Fix \Drupal\Tests\Core\Test\TestSetupTraitTest::testChangeDatabasePrefix() on PHP 8.2

Issue #3254726 by longwave, mondrake: Remove SimpleTest support from run-tests.sh, TestDiscovery and TestRunnerKernel

Issue #3222251 by bbrala, longwave: [November 8, 2021] Replace all isset constructs with the null coalescing operator

Issue #3106531 by mondrake, daffie, Rithesh BK, catch, xjm: Notify in Status Report that per-table database prefixes are no longer supported, and will throw errors in Drupal 10.0

Issue #3177120 by anmolgoyal74, Pooja Ganjage, paulocs, markdorison, walangitan, longwave: Remove references to WebTestBase

Issue #2619482 by cburschka, ankit.singh, ravi.shankar, jungle, daffie: Convert all get_called_class()/get_class() to static::

Issue #3081501 by Mile23, Wim Leers, alexpott: Remove TestSetupTrait::$originalProfile and test infrastructure which uses it

Issue #2987124 by alexpott, mondrake: Functional tests don't use SIMPLETEST_DB environmental variable as expected

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

Issue #2754217 by alexpott, xjm, dawehner, martin107: Random Test Failure with "failed to open stream" for temporary://.htaccess

Issue #2796105 by larowlan, Sam152, Yogesh Pawar, alexpott, dawehner, anish.a, Fabianx: Move similar methods in BrowserTestBase / WebTestBase to a trait; untangle installDrupal()