Better tests for php-nextgen (#16569)

* better tests for php nextgen

* add new files

samples/client/echo_api/php-nextgen/src/Model/ModelInterface.php

@@ -0,0 +1,112 @@
+<?php
+/**
+ * ModelInterface
+ *
+ * PHP version 8.1
+ *
+ * @category Class
+ * @package  OpenAPI\Client\Model
+ * @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
+ * Do not edit the class manually.
+ */
+
+namespace OpenAPI\Client\Model;
+
+/**
+ * Interface abstracting model access.
+ *
+ * @package OpenAPI\Client\Model
+ * @author  OpenAPI Generator team
+ */
+interface ModelInterface
+{
+    /**
+     * The original name of the model.
+     *
+     * @return string
+     */
+    public function getModelName();
+
+    /**
+     * Array of property to type mappings. Used for (de)serialization
+     *
+     * @return array
+     */
+    public static function openAPITypes();
+
+    /**
+     * Array of property to format mappings. Used for (de)serialization
+     *
+     * @return array
+     */
+    public static function openAPIFormats();
+
+    /**
+     * Array of attributes where the key is the local name, and the value is the original name
+     *
+     * @return array
+     */
+    public static function attributeMap();
+
+    /**
+     * Array of attributes to setter functions (for deserialization of responses)
+     *
+     * @return array
+     */
+    public static function setters();
+
+    /**
+     * Array of attributes to getter functions (for serialization of requests)
+     *
+     * @return array
+     */
+    public static function getters();
+
+    /**
+     * Show all the invalid properties with reasons.
+     *
+     * @return array
+     */
+    public function listInvalidProperties();
+
+    /**
+     * Validate all the properties in the model
+     * return true if all passed
+     *
+     * @return bool
+     */
+    public function valid();
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool;
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool;
+}