diff --git a/core/modules/system/src/Tests/Cache/AssertPageCacheContextsAndTagsTrait.php b/core/modules/system/src/Tests/Cache/AssertPageCacheContextsAndTagsTrait.php
index 6841293..c943c98 100644
--- a/core/modules/system/src/Tests/Cache/AssertPageCacheContextsAndTagsTrait.php
+++ b/core/modules/system/src/Tests/Cache/AssertPageCacheContextsAndTagsTrait.php
@@ -25,6 +25,15 @@ protected function enablePageCaching() {
     $config->save();
   }
 
+  /**
+   * Gets a specifc header value as array.
+   *
+   * @param string $header_name
+   *   The header name.
+   *
+   * @return array
+   *   The header value, potentially exploded by spaces.
+   */
   protected function getCacheHeaderValues($header_name) {
     $header_value = $this->drupalGetHeader($header_name);
     if (empty($header_value)) {
@@ -73,6 +82,12 @@ protected function assertPageCacheContextsAndTags(Url $url, array $expected_cont
     }
   }
 
+  /**
+   * Ensures that some cache tags got sent in the latest response.
+   *
+   * @param array $expected_tags
+   *   The expected tags.
+   */
   protected function assertCacheTags(array $expected_tags) {
     $actual_tags = $this->getCacheHeaderValues('X-Drupal-Cache-Tags');
     $this->assertIdentical($actual_tags, $expected_tags);
@@ -82,6 +97,12 @@ protected function assertCacheTags(array $expected_tags) {
     }
   }
 
+  /**
+   * Ensures that some cache contexts got sent in the latest response.
+   *
+   * @param array $expected_contexts
+   *   The expected cache contexts.
+   */
   protected function assertCacheContexts(array $expected_contexts) {
     $actual_contexts = $this->getCacheHeaderValues('X-Drupal-Cache-Contexts');
     $this->assertIdentical($actual_contexts, $expected_contexts);