Converted existing content negotiation tests to new syntax.

Fixed: Integration tests used to send request body "null" on GET requests, while they should not send a body at all.

Author: Bart Koelman

Diff for: test/JsonApiDotNetCoreExampleTests/Acceptance/Spec/ContentNegotiationTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Threading.Tasks;
@@ -102,42 +103,66 @@ public async Task RunOnDatabaseAsync(Func<TDbContext, Task> asyncAction)
         }
 
         public async Task<(HttpResponseMessage httpResponse, TResponseDocument responseDocument)>
-            ExecuteGetAsync<TResponseDocument>(string requestUrl)
+            ExecuteGetAsync<TResponseDocument>(string requestUrl,
+                IEnumerable<MediaTypeWithQualityHeaderValue> acceptHeaders = null)
         {
-            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Get, requestUrl);
+            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Get, requestUrl, null, null, acceptHeaders);
         }
 
         public async Task<(HttpResponseMessage httpResponse, TResponseDocument responseDocument)>
-            ExecutePostAsync<TResponseDocument>(string requestUrl, object requestBody)
+            ExecutePostAsync<TResponseDocument>(string requestUrl, object requestBody,
+                string contentType = HeaderConstants.MediaType,
+                IEnumerable<MediaTypeWithQualityHeaderValue> acceptHeaders = null)
         {
-            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Post, requestUrl, requestBody);
+            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Post, requestUrl, requestBody, contentType,
+                acceptHeaders);
         }
 
         public async Task<(HttpResponseMessage httpResponse, TResponseDocument responseDocument)>
-            ExecutePatchAsync<TResponseDocument>(string requestUrl, object requestBody)
+            ExecutePatchAsync<TResponseDocument>(string requestUrl, object requestBody,
+                string contentType = HeaderConstants.MediaType,
+                IEnumerable<MediaTypeWithQualityHeaderValue> acceptHeaders = null)
         {
-            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Patch, requestUrl, requestBody);
+            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Patch, requestUrl, requestBody, contentType,
+                acceptHeaders);
         }
 
         public async Task<(HttpResponseMessage httpResponse, TResponseDocument responseDocument)>
-            ExecuteDeleteAsync<TResponseDocument>(string requestUrl, object requestBody = null)
+            ExecuteDeleteAsync<TResponseDocument>(string requestUrl, object requestBody = null,
+                string contentType = HeaderConstants.MediaType,
+                IEnumerable<MediaTypeWithQualityHeaderValue> acceptHeaders = null)
         {
-            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Delete, requestUrl, requestBody);
+            return await ExecuteRequestAsync<TResponseDocument>(HttpMethod.Delete, requestUrl, requestBody, contentType,
+                acceptHeaders);
         }
 
         private async Task<(HttpResponseMessage httpResponse, TResponseDocument responseDocument)>
-            ExecuteRequestAsync<TResponseDocument>(HttpMethod method, string requestUrl, object requestBody = null)
+            ExecuteRequestAsync<TResponseDocument>(HttpMethod method, string requestUrl, object requestBody,
+                string contentType, IEnumerable<MediaTypeWithQualityHeaderValue> acceptHeaders)
         {
             var request = new HttpRequestMessage(method, requestUrl);
             string requestText = SerializeRequest(requestBody);
 
             if (!string.IsNullOrEmpty(requestText))
             {
                 request.Content = new StringContent(requestText);
-                request.Content.Headers.ContentType = new MediaTypeHeaderValue(HeaderConstants.MediaType);
+
+                if (contentType != null)
+                {
+                    request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse(contentType);
+                }
             }
 
             using HttpClient client = Factory.CreateClient();
+
+            if (acceptHeaders != null)
+            {
+                foreach (var acceptHeader in acceptHeaders)
+                {
+                    client.DefaultRequestHeaders.Accept.Add(acceptHeader);
+                }
+            }
+
             HttpResponseMessage responseMessage = await client.SendAsync(request);
 
             string responseText = await responseMessage.Content.ReadAsStringAsync();
@@ -148,11 +173,11 @@ public async Task RunOnDatabaseAsync(Func<TDbContext, Task> asyncAction)
 
         private string SerializeRequest(object requestBody)
         {
-            string requestText = requestBody is string stringRequestBody
-                ? stringRequestBody
-                : JsonConvert.SerializeObject(requestBody);
-
-            return requestText;
+            return requestBody == null
+                ? null
+                : requestBody is string stringRequestBody
+                    ? stringRequestBody
+                    : JsonConvert.SerializeObject(requestBody);
         }
 
         private TResponseDocument DeserializeResponse<TResponseDocument>(string responseText)