RequiredTest is not testing what it thinks it is testing.

Nice catch.

1. +++ b/core/modules/system/tests/src/Functional/Module/UninstallTest.php
   @@ -57,6 +57,17 @@ public function testUninstallPage() {
        $this->assertTitle(t('Uninstall') . ' | Drupal');
   

   t() in a test.

2. +++ b/core/modules/system/tests/src/Functional/Module/UninstallTest.php
   @@ -57,6 +57,17 @@ public function testUninstallPage() {
   +    foreach (\Drupal::service('extension.list.module')->getAllInstalledInfo() as $module => $info) {
   

   Grab the service from $this->container

2. I don't think there is any difference between \Drupal::service() and $this->container. And we have no rules about what to use.

Nope, just lively discussions on the subject

Feedback has been addressed. The old test never actually added a required module, so if we ever got to a state where a test install had no required modules it would pass and never test anything, the new version also fixes this gap, nice!

"And we have no rules about what to use."

Right, so use $this->container. :-)

No worries. RTBC is fine.

Committed/pushed to 8.6.x and cherry-picked to 8.5.x. Thanks!

This broke 8.5.x as #2208429: Extension System, Part III: ExtensionList, ModuleExtensionList and ProfileExtensionList never went into 8.5.x.

https://www.drupal.org/pift-ci-job/918609

Drupal\Tests\system\Functional\Module\UninstallTest::testUninstallPage
Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: You have requested a non-existent service "extension.list.module".