diff --git a/core/tests/Drupal/Tests/Core/Menu/LocalTaskIntegrationTest.php b/core/tests/Drupal/Tests/Core/Menu/LocalTaskIntegrationTest.php
index b0aa33e..9106f77 100644
--- a/core/tests/Drupal/Tests/Core/Menu/LocalTaskIntegrationTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/LocalTaskIntegrationTest.php
@@ -89,6 +89,12 @@ protected function getLocalTaskManager($module_dirs, $route_name, $route_params)
     $property = new \ReflectionProperty('Drupal\Core\Menu\LocalTaskManager', 'moduleHandler');
     $property->setAccessible(TRUE);
     $property->setValue($manager, $module_handler);
+    // Set all the modules as being existant.
+    $module_handler->expects($this->any())
+      ->method('moduleExists')
+      ->will($this->returnCallback(function ($module) use ($module_dirs) {
+        return isset($module_dirs[$module]);
+      }));
 
     $pluginDiscovery = new YamlDiscovery('local_tasks', $module_dirs);
     $pluginDiscovery = new ContainerDerivativeDiscoveryDecorator($pluginDiscovery);