Issue #3504114: Test to demo error

core/lib/Drupal/Core/Cache/Context/PseudoCacheContext.php

+<?php
+
+namespace Drupal\Core\Cache\Context;
+
+use Drupal\Core\Cache\CacheableMetadata;
+
+/**
+ * Defines the PseudoCacheContext service.
+ *
+ * This cache context will always return the value of '1', but is not intended
+ * to be added manually. Instead, users are expected to use the associated
+ * helper class \Drupal\Core\Cache\DependencyVariation instead.
+ *
+ * Cache context ID: 'pseudo'.
+ *
+ * @see \Drupal\Core\Cache\DependencyVariation
+ */
+class PseudoCacheContext implements CalculatedCacheContextInterface {
+
+  const ID = 'pseudo';
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel() {
+    return t('Pseudo');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext($parameter = NULL) {
+    return 1;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata($parameter = NULL) {
+    return new CacheableMetadata();
+  }
+
+}