[JavaScript] Add petstore integration test to JS ES6 client (OAS3) (#2245)

* add test for js es6 oas3 client

* fix test with proper done

* add test, fix servers index check

samples/openapi3/client/petstore/javascript-es6/docs/FakeApi.md

@@ -4,6 +4,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
+[**fakeHealthGet**](FakeApi.md#fakeHealthGet) | **GET** /fake/health | Health check endpoint
 [**fakeOuterBooleanSerialize**](FakeApi.md#fakeOuterBooleanSerialize) | **POST** /fake/outer/boolean | 
 [**fakeOuterCompositeSerialize**](FakeApi.md#fakeOuterCompositeSerialize) | **POST** /fake/outer/composite | 
 [**fakeOuterNumberSerialize**](FakeApi.md#fakeOuterNumberSerialize) | **POST** /fake/outer/number | 
@@ -18,6 +19,42 @@ Method | HTTP request | Description
 [**testJsonFormData**](FakeApi.md#testJsonFormData) | **GET** /fake/jsonFormData | test json serialization of form data
 
 
+<a name="fakeHealthGet"></a>
+# **fakeHealthGet**
+> HealthCheckResult fakeHealthGet()
+
+Health check endpoint
+
+### Example
+```javascript
+import OpenApiPetstore from 'open_api_petstore';
+
+let apiInstance = new OpenApiPetstore.FakeApi();
+apiInstance.fakeHealthGet((error, data, response) => {
+  if (error) {
+    console.error(error);
+  } else {
+    console.log('API called successfully. Returned data: ' + data);
+  }
+});
+```
+
+### Parameters
+This endpoint does not need any parameter.
+
+### Return type
+
+[**HealthCheckResult**](HealthCheckResult.md)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: Not defined
+ - **Accept**: application/json
+
 <a name="fakeOuterBooleanSerialize"></a>
 # **fakeOuterBooleanSerialize**
 > Boolean fakeOuterBooleanSerialize(opts)

samples/openapi3/client/petstore/javascript-es6/docs/HealthCheckResult.md

@@ -0,0 +1,8 @@
+# OpenApiPetstore.HealthCheckResult
+
+## Properties
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**nullableMessage** | **String** |  | [optional] 
+
+