[10.x] Fix parallel testing without any database connection

src/Illuminate/Testing/Concerns/TestDatabases.php

@@ -141,6 +141,10 @@ protected function usingDatabase($database, $callable)
      */
     protected function whenNotUsingInMemoryDatabase($callback)
     {
+        if (ParallelTesting::option('without_databases')) {
+            return;
+        }
+
         $database = DB::getConfig('database');
 
         if ($database !== ':memory:') {

tests/Integration/Testing/TestWithoutDatabaseParallelTest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Testing;
+
+use Illuminate\Support\Facades\ParallelTesting;
+use Illuminate\Testing\ParallelTestingServiceProvider;
+use Orchestra\Testbench\TestCase;
+
+class TestWithoutDatabaseParallelTest extends TestCase
+{
+    protected function getPackageProviders($app)
+    {
+        return [ParallelTestingServiceProvider::class];
+    }
+
+    public function testRunningParallelTestWithoutDatabaseShouldNotCrashOnDefaultConnection()
+    {
+        // Given an application that does not use database connections at all
+        $this->app['config']->set('database.default', null);
+
+        // When we run parallel testing with `without-databases` option
+        $_SERVER['LARAVEL_PARALLEL_TESTING'] = 1;
+        $_SERVER['LARAVEL_PARALLEL_TESTING_WITHOUT_DATABASES'] = 1;
+        $_SERVER['TEST_TOKEN'] = '1';
+
+        // We should not create a database connection to check if it's SQLite or not.
+        ParallelTesting::callSetUpProcessCallbacks();
+    }
+}