Remove BC layer for TestSetupTrait

3 are core tests, remains are simpletest

Can't get how to fix 2 remaining but there 2 more down

Reroll following the removal of Simpletest.

+++ b/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
@@ -37,6 +37,13 @@ class TestSiteInstallCommand extends Command {
+  /**
+   * The theme to install as the default.
+   *
+   * @var string
+   */
+  protected $defaultTheme = 'stark';

So I'm not sure this is the correct change.

I think we should remove the calls to

 $this->installDefaultThemeFromClassProperty($container);
    $this->installModulesFromClassProperty($container);

in \Drupal\TestSite\Commands\TestSiteInstallCommand::installDrupal() - they look meaningless as this is not a test and you don't inherit from it.

To maintain BC we should install classy and set it as the default theme in \Drupal\TestSite\Commands\TestSiteInstallCommand::installDrupal() and then we should file an issue to discuss the default theme in tests (like Nightwatch) that use this command.

Postponing this on #3115903: Remove test cruft from TestSiteInstallCommand which addresses #13

#3115903: Remove test cruft from TestSiteInstallCommand has been committed.

Reroll following #3115903: Remove test cruft from TestSiteInstallCommand, removing the change to TestSiteInstallCommand.

Fix the test (LegacyStyleSheetsRemoveTest) and I think we could use @inheritdoc because variable defined in parent class
New exception also documented

Thanks @andypost, changes look good to me and I agree we can use inheritdoc.

+++ b/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
@@ -400,6 +400,9 @@ protected function initKernel(Request $request) {
+   * @throws \Exception

@@ -420,11 +423,7 @@ protected function installDefaultThemeFromClassProperty(ContainerInterface $cont
+      throw new \Exception('Drupal\Tests\BrowserTestBase::$defaultTheme is required. See https://www.drupal.org/node/3083055, which includes recommendations on which theme to use.');

I wonder if we should use InvalidArgumentException or DomainException https://www.php.net/manual/en/class.domainexception.php

@andypost I just pushed and x-posted with you. Feel free to open a follow-up. I don;t think this matters because you're not going to be catching this exception in calling code and doing something else - you going to be fixing your test and moving on.

Committed 305c401 and pushed to 9.0.x. Thanks!

NP, thank you! That's surely runtime exception so no reason to followup