Better tests for php-nextgen (#16569)

* better tests for php nextgen

* add new files

samples/client/echo_api/php-nextgen/tests/Model/StringEnumRefTest.php

@@ -0,0 +1,82 @@
+<?php
+/**
+ * StringEnumRefTest
+ *
+ * PHP version 8.1
+ *
+ * @category Class
+ * @package  OpenAPI\Client
+ * @author   OpenAPI Generator team
+ * @link     https://openapi-generator.tech
+ */
+
+/**
+ * Echo Server API
+ *
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ * @generated Generated by: https://openapi-generator.tech
+ * OpenAPI Generator version: 7.0.1-SNAPSHOT
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Please update the test case below to test the model.
+ */
+
+namespace OpenAPI\Client\Test\Model;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * StringEnumRefTest Class Doc Comment
+ *
+ * @category    Class
+ * @description StringEnumRef
+ * @package     OpenAPI\Client
+ * @author      OpenAPI Generator team
+ * @link        https://openapi-generator.tech
+ */
+class StringEnumRefTest extends TestCase
+{
+
+    /**
+     * Setup before running any test case
+     */
+    public static function setUpBeforeClass(): void
+    {
+    }
+
+    /**
+     * Setup before running each test case
+     */
+    public function setUp(): void
+    {
+    }
+
+    /**
+     * Clean up after running each test case
+     */
+    public function tearDown(): void
+    {
+    }
+
+    /**
+     * Clean up after running all test cases
+     */
+    public static function tearDownAfterClass(): void
+    {
+    }
+
+    /**
+     * Test "StringEnumRef"
+     */
+    public function testStringEnumRef()
+    {
+        // TODO: implement
+        $this->markTestIncomplete('Not implemented');
+    }
+}