Add the Author entity for the testGetMockForModelWithPlugin test

tests/test_app/Plugin/TestPlugin/src/Model/Entity/Author.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace TestPlugin\Model\Entity;
+
+use Cake\ORM\Entity;
+
+/**
+ * Tests entity class used for asserting correct entity is loaded
+ *
+ */
+class Author extends Entity {
+
+}