diff -u b/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
--- b/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -1061,10 +1061,9 @@
       $this->prepareDatabasePrefix();
     }

-    // Clone the current connection and replace the current prefix.
-    $connection_info = Database::getConnectionInfo('default');
-    if (is_null($connection_info)) {
-      $db_url = getenv('SIMPLETEST_DB');
+    // If the test is run with argument dburl then use it.
+    $db_url = defined('SIMPLETEST_DB') ? getenv('SIMPLETEST_DB') : '';
+    if (!empty($db_url)) {
       $info = parse_url($db_url);
       if (!isset($info['scheme'], $info['host'], $info['path'])) {
         throw new \InvalidArgumentException('Invalid --dburl. Minimum requirement: driver://host/database.');
@@ -1095,6 +1094,12 @@
       }
       Database::addConnectionInfo('default', 'default', $database);
     }
+
+    // Clone the current connection and replace the current prefix.
+    $connection_info = Database::getConnectionInfo('default');
+    if (is_null($connection_info)) {
+      throw new \InvalidArgumentException('There is no database connection so no tests can be run.');
+    }
     else {
       Database::renameConnection('default', 'simpletest_original_default');
       foreach ($connection_info as $target => $value) {