add a test/helper method for loading Plugins with Application

src/TestSuite/TestCase.php

@@ -17,6 +17,7 @@
 use Cake\Core\Configure;
 use Cake\Datasource\ConnectionManager;
 use Cake\Event\EventManager;
+use Cake\Http\BaseApplication;
 use Cake\ORM\Entity;
 use Cake\ORM\Exception\MissingTableClassException;
 use Cake\ORM\Locator\LocatorAwareTrait;
@@ -189,6 +190,34 @@ public function loadFixtures()
         }
     }
 
+    /**
+     * simulate running the Application
+     * @param string|array list of Plugins to load
+     * @return \Cake\Http\BaseApplication
+     */
+    public function loadPlugins($plugins = [])
+    {
+        $app = $this->getMockForAbstractClass(
+            BaseApplication::class,
+            ['']
+        );
+
+        if (is_string($plugins)) {
+            $plugins = (array)$plugins;
+        }
+        foreach ($plugins as $k => $opts) {
+            if (is_array($opts)) {
+                $app->addPlugin($k, $opts);
+            } else {
+                $app->addPlugin($opts);
+            }
+        }
+        $app->pluginBootstrap();
+        $builder = Router::createRouteBuilder('/');
+        $app->pluginRoutes($builder);
+        return $app;
+    }
+
     /**
      * Asserts that a global event was fired. You must track events in your event manager for this assertion to work
      *