Add test for relative root in links

Signed-off-by: Tobias Grasse <tg@glancr.de>

Author: tobias-grasse

test/controllers/controller_test.rb

@@ -10,6 +10,12 @@ def setup
     JSONAPI.configuration.always_include_to_one_linkage_data = false
   end
 
+  def test_links_include_relative_root
+    Rails.application.config.relative_url_root = '/subdir'
+    assert_cacheable_get :index
+    assert json_response['data'][0]['links']['self'].include?('/subdir')
+  end
+
   def test_index
     assert_cacheable_get :index
     assert_response :success