diff --git a/core/tests/Drupal/FunctionalTests/ExistingDrupal8StyleDatabaseConnectionInSettingsPhpTest.php b/core/tests/Drupal/FunctionalTests/ExistingDrupal8StyleDatabaseConnectionInSettingsPhpTest.php
index 855387f695..e49f3ee7e9 100644
--- a/core/tests/Drupal/FunctionalTests/ExistingDrupal8StyleDatabaseConnectionInSettingsPhpTest.php
+++ b/core/tests/Drupal/FunctionalTests/ExistingDrupal8StyleDatabaseConnectionInSettingsPhpTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\FunctionalTests;
 
+use Drupal\Core\Database\Connection;
 use Drupal\Core\Database\Database;
 use Drupal\Tests\BrowserTestBase;
 
@@ -35,6 +36,19 @@ protected function setUp(): void {
     $namespace_search = "'namespace' => 'Drupal\\\\$driver\\\\Driver\\\\Database\\\\$driver',";
     $namespace_replace = "'namespace' => 'Drupal\\\\Core\\\\Database\\\\Driver\\\\$driver',";
     $contents = str_replace($namespace_search, $namespace_replace, $contents);
+
+    // Add a replica connection to the database settings.
+    $contents .= "\$databases['default']['replica'][] = array (\n";
+    $contents .= "  'database' => 'dbtest',\n";
+    $contents .= "  'username' => 'db',\n";
+    $contents .= "  'password' => 'db',\n";
+    $contents .= "  'prefix' => 'test22806835',\n";
+    $contents .= "  'host' => 'db',\n";
+    $contents .= "  'port' => 3306,\n";
+    $contents .= "  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',\n";
+    $contents .= "  'driver' => 'mysql',\n";
+    $contents .= ");\n";
+
     file_put_contents($filename, $contents);
   }
 
@@ -56,4 +70,14 @@ public function testExistingDrupal8StyleDatabaseConnectionInSettingsPhp() {
     $this->assertStringNotContainsString("'autoload' => 'core/modules/$driver/src/Driver/Database/$driver/", $contents);
   }
 
+  /**
+   * Confirms that the replica database connection works.
+   */
+  public function testReplicaDrupal8StyleDatabaseConnectionInSettingsPhp() {
+    $this->drupalLogin($this->drupalCreateUser());
+
+    $replica = Database::getConnection('replica', 'default');
+    $this->assertInstanceOf(Connection::class, $replica);
+  }
+
 }