--- /dev/null
+<?php
+
+namespace Drupal\theme_test\Theme;
+
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Theme\ThemeNegotiatorInterface;
+
+/**
+ * Implements a test theme negotiator which was configured with a high priority.
+ */
+class HighPriorityThemeNegotiator implements ThemeNegotiatorInterface {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function applies(RouteMatchInterface $route_match) {
+ return ($route_match->getRouteName() == 'theme_test.priority');
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function determineActiveTheme(RouteMatchInterface $route_match) {
+ return 'classy';
+ }
+
+}