diff --git a/core/lib/Drupal/Core/Test/TestDatabase.php b/core/lib/Drupal/Core/Test/TestDatabase.php
index 42a90c0fd6..e126b3aca4 100644
--- a/core/lib/Drupal/Core/Test/TestDatabase.php
+++ b/core/lib/Drupal/Core/Test/TestDatabase.php
@@ -118,18 +118,19 @@ public function getDatabasePrefix() {
    *   The unique lock ID for the test method.
    */
   protected function getTestLock($create_lock = FALSE) {
-    // If we're only running with a concurrency of greater than 1 there is a
-    // risk the random number generated clashing. Therefore we need to create
-    // a lock.
+    // There is a risk that the generated random number is a duplicate. This
+    // would cause different tests to try to use the same database prefix.
+    // Therefore, if running with a concurrency of greater than 1, we need to
+    // create a lock.
     if (getenv('RUN_TESTS_CONCURRENCY') > 1) {
       $create_lock = TRUE;
     }
 
-    // Ensure that the generated lock ID is not in use, which may happen when
-    // tests are run concurrently.
     do {
       $lock_id = mt_rand(10000000, 99999999);
       if ($create_lock && @symlink(__FILE__, $this->getLockFile($lock_id)) === FALSE) {
+        // If we can't create a symlink, the lock ID is in use. Generate another
+        // one. Symlinks are used because they are atomic and reliable.
         $lock_id = NULL;
       }
     } while ($lock_id === NULL);
diff --git a/core/scripts/test-site.php b/core/scripts/test-site.php
index 3e33fabcda..1244f4bf29 100644
--- a/core/scripts/test-site.php
+++ b/core/scripts/test-site.php
@@ -18,5 +18,7 @@
 putenv('SYMFONY_DEPRECATIONS_HELPER=disabled');
 require_once __DIR__ . '/../tests/bootstrap.php';
 
+// The application version is 0.1.0 to indicate that it is for internal use only
+// and not currently API.
 $app = new TestSiteApplication('test-site', '0.1.0');
 $app->run();
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
index 6f122d8a19..c93823fa65 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteInstallCommand.php
@@ -41,6 +41,8 @@ class TestSiteInstallCommand extends Command {
   /**
    * Time limit in seconds for the test.
    *
+   * Used by \Drupal\Core\Test\FunctionalTestSetupTrait::prepareEnvironment().
+   *
    * @var int
    */
   protected $timeLimit = 500;
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
index 4be43788f7..5c64df38e0 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteReleaseLocksCommand.php
@@ -10,6 +10,9 @@
 /**
  * Command to release all test site database prefix locks.
  *
+ * Note that this command can't be safely tested by DrupalCI without potentially
+ * causing random failures.
+ *
  * @internal
  */
 class TestSiteReleaseLocksCommand extends Command {
diff --git a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
index e2f355b603..ea776c3061 100644
--- a/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
+++ b/core/tests/Drupal/TestSite/Commands/TestSiteTearDownCommand.php
@@ -94,7 +94,7 @@ protected function tearDown(TestDatabase $test_database, $db_url) {
   /**
    * Deletes all files and directories in the specified path recursively.
    *
-   * Note this version has no dependencies on Drupal core to ensure that the
+   * Note this method has no dependencies on Drupal core to ensure that the
    * test site can be torn down even if something in the test site is broken.
    *
    * @param string $path
diff --git a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
index 4c2444ef08..0eff417d29 100644
--- a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
+++ b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
@@ -177,19 +177,6 @@ public function testInstallScript() {
     // is released during tear down.
     $this->assertFileExists($this->getTestLockFile($db_prefix));
     $this->assertFileNotExists($this->getTestLockFile($other_db_prefix));
-
-    // Release all locks.
-    $command_line = $php_binary_path . ' core/scripts/test-site.php release-locks';
-    $process = new Process($command_line, $this->root);
-    // Set the timeout to a value that allows debugging.
-    $process->setTimeout(500);
-    $process->run();
-    $this->assertSame(0, $process->getExitCode());
-    $this->assertContains("Successfully released all the test database locks", $process->getOutput());
-
-    // Both tests sites' locks should no longer exist now.
-    $this->assertFileNotExists($this->getTestLockFile($db_prefix));
-    $this->assertFileNotExists($this->getTestLockFile($other_db_prefix));
   }
 
   /**