Start transactions before the app is fully booted. (#11)

This make a cleaner state more likely, and ensures that settings set via `$this->setting` are cleaned up after the test case runs.

php-packages/testing/src/integration/Extend/BeginTransactionAndSetDatabase.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Flarum\Testing\integration\Extend;
+
+use Flarum\Extend\ExtenderInterface;
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+use Illuminate\Database\ConnectionInterface;
+
+class BeginTransactionAndSetDatabase implements ExtenderInterface
+{
+    /**
+     * A callback to set the database connection object on the test case.
+     */
+    protected $setDbOnTestCase;
+
+    public function __construct(callable $setDbOnTestCase)
+    {
+        $this->setDbOnTestCase = $setDbOnTestCase;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $db = $container->make(ConnectionInterface::class);
+
+        $db->beginTransaction();
+
+        ($this->setDbOnTestCase)($db);
+    }
+}