Move integration tests to separate directory

Again, we do all of this to prepare for creating "real" test suites for
each type of tests.

tests/integration/api/Controller/ApiControllerTestCase.php

@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration\api\Controller;
+
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+use Flarum\User\User;
+use Illuminate\Support\Arr;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+abstract class ApiControllerTestCase extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+    /**
+     * @var RequestHandlerInterface
+     */
+    protected $controller;
+
+    /**
+     * @var null|User
+     */
+    protected $actor = null;
+
+    protected function callWith(array $body = [], array $queryParams = []): ResponseInterface
+    {
+        if (! Arr::get($body, 'data') && Arr::isAssoc($body)) {
+            $body = ['data' => ['attributes' => $body]];
+        }
+
+        return $this->call(
+            $this->controller,
+            $this->actor,
+            $queryParams,
+            $body
+        );
+    }
+
+    protected function tearDown()
+    {
+        $this->actor = null;
+        parent::tearDown();
+    }
+}