upd: ApiPlatformTestCase & doc

README.md

@@ -422,14 +422,21 @@ asserts this number of messages to be dispatched to the message bus
 <tr>
 <td>dispatchedMessages</td>
 <td>
-array of message classes, asserts that at least one instance of each given class 
-has been dispatched to the message bus
+Array of message classes, asserts that at least one instance of each given class 
+has been dispatched to the message bus. An Element can also be an array of
+[FQCN, callable], in that case the callback is called for each matching message
+with that message as first parameter and the JSON response as second parameter,
+to trigger additional assertions for the message.
 </td>
 <td>
 
 ```php
 'dispatchedMessages' => [
   TenantCreatedMessage::class,
+
+  [TenantCreatedMessage::class, function (object $message, array $data): void {
+      self::assertSame($data['id'], $message->tenantId);
+  }]
 ],
 ```
 

src/PHPUnit/ApiPlatformTestCase.php

@@ -124,7 +124,7 @@ abstract class ApiPlatformTestCase extends ApiTestCase
     public const HYDRA_PROBLEM_403 = [
         '@id'               => '/errors/403',
         '@type'             => 'hydra:Error',
-        'hydra:description' => '@todo',
+        // 'hydra:description' => '', // varies
         'hydra:title'       => 'An error occurred',
     ] + self::PROBLEM_403;
     public const HYDRA_PROBLEM_ACCESS_DENIED = [
@@ -211,7 +211,11 @@ abstract class ApiPlatformTestCase extends ApiTestCase
      * messageCount:       asserts this number of messages to be dispatched
      *                     to the message bus
      * dispatchedMessages: array of message classes, asserts that at least one instance
-     *                     of each given class has been dispatched to the message bus
+     *                     of each given class has been dispatched to the message bus.
+     *                     Instead of class names the elements can be an array of
+     *                     [classname, callable]. This callback will be called
+     *                     (for each matching message) with the message as first
+     *                     parameter and the returned JSON as second parameter.
      * skipRefresh:        if true the database will not be refreshed before
      *                     the operation, to allow calling testOperation()
      *                     multiple times after each other in one testcase