More unittests

tests/Plugin/PluginManagerTest.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Spark\Plugin;
+
+use SparkPlug;
+
+class PluginManagerTest extends \PhpUnit\Framework\TestCase
+{
+    
+    /**
+     * @covers PluginManager::registerPlugin
+     * @covers PluginManager::getPlugin
+     */
+    public function testRegisteringAndFetchingPlugin()
+    {
+        $manager = new PluginManager();
+
+        $plugin = new TestPlugin();
+        $manager->registerPlugin('test.testplugin', $plugin);
+
+        $gplugin = $manager->getPlugin('test.testplugin');
+
+        $this->assertEquals($plugin, $gplugin);
+    }
+}
+
+class TestPlugin extends SparkPlug
+{
+    public function load()
+    {}
+}