feat(test): test related post

tests/src/Functional/JsonExtrasApiFunctionalTest.php

@@ -173,6 +173,22 @@ class JsonExtrasApiFunctionalTest extends JsonApiFunctionalTestBase {
     $date = new \DateTime($body['data']['attributes']['updatedAt']);
     $created_node = Node::load($created_response['data']['attributes']['internalId']);
     $this->assertSame((int) $date->format('U'), (int) $created_node->getChangedTime());
+
+    // 2. Successful relationships PATCH.
+    $uuid = $created_response['data']['id'];
+    $relationships_url = Url::fromUserInput('/api/articles/' . $uuid . '/relationships/tags');
+    $body = [
+      'data' => [
+        ['type' => 'taxonomy_term--tags', 'id' => $this->tags[2]->uuid()]
+      ],
+    ];
+    $response = $this->request('POST', $relationships_url, [
+      'body' => Json::encode($body),
+      'auth' => [$this->user->getUsername(), $this->user->pass_raw],
+      'headers' => ['Content-Type' => 'application/vnd.api+json'],
+    ]);
+    $created_response = Json::decode((string) $response->getBody());
+    $this->assertCount(3, $created_response['data']);
   }
 
   /**