diff --git a/tests/src/Functional/ResourceTestBase.php b/tests/src/Functional/ResourceTestBase.php
index edf0ac2..e139717 100644
--- a/tests/src/Functional/ResourceTestBase.php
+++ b/tests/src/Functional/ResourceTestBase.php
@@ -1599,6 +1599,8 @@ abstract class ResourceTestBase extends BrowserTestBase {
    *   The base URL with which to test includes.
    * @param array $request_options
    *   Request options to apply.
+   *
+   * @see \GuzzleHttp\ClientInterface::request()
    */
   protected function doTestSparseFieldSets(Url $url, array $request_options) {
     foreach ($this->getSparseFieldSets() as $type => $field_set) {
@@ -1647,6 +1649,8 @@ abstract class ResourceTestBase extends BrowserTestBase {
    *   The base URL with which to test includes.
    * @param array $request_options
    *   Request options to apply.
+   *
+   * @see \GuzzleHttp\ClientInterface::request()
    */
   protected function doTestIncluded(Url $url, array $request_options) {
     $individual_response = $this->request('GET', $url, $request_options);
@@ -1818,6 +1822,8 @@ abstract class ResourceTestBase extends BrowserTestBase {
    *
    * @return array
    *   The related ResourceResponses, keyed by relationship field names.
+   *
+   * @see \GuzzleHttp\ClientInterface::request()
    */
   protected function getRelatedResponses(array $links, array $request_options) {
     return array_reduce(array_keys($links), function ($related_responses, $field_name) use ($links, $request_options) {