diff --git a/core/modules/update/tests/fixtures/release-history/drupal.broken.xml b/core/modules/update/tests/fixtures/release-history/drupal.broken.xml
index 1ba5d5e408acf5191e4c309a5cc643e69c6fc83a..01e7ce2a0f13f2ddc28140555db3c4c86da8ec9a 100644
--- a/core/modules/update/tests/fixtures/release-history/drupal.broken.xml
+++ b/core/modules/update/tests/fixtures/release-history/drupal.broken.xml
@@ -1,3 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
+<!--
+This XML file is empty to test no information scenarios.
+-->
 <project xmlns:dc="http://purl.org/dc/elements/1.1/">
 </project>
diff --git a/core/modules/update/tests/src/Functional/UpdateSemverCoreTest.php b/core/modules/update/tests/src/Functional/UpdateSemverCoreTest.php
index 8ac038ed83a86e5d4fbe513df9b6e44157e0f96b..0566b44e552fea03ac110428e8a990ed29f03064 100644
--- a/core/modules/update/tests/src/Functional/UpdateSemverCoreTest.php
+++ b/core/modules/update/tests/src/Functional/UpdateSemverCoreTest.php
@@ -77,6 +77,11 @@ public function testFetchTasks() {
 
   /**
    * Checks that Drupal recovers after problems connecting to update server.
+   *
+   * This test uses the following XML fixtures.
+   *  - drupal.broken.xml
+   *  - drupal.sec.8.0.2.xml
+   *     'supported_branches' is '8.0.,8.1.'.
    */
   public function testBrokenThenFixedUpdates() {
     $this->drupalLogin($this->drupalCreateUser([