diff --git a/tests/test_framework/phpbb_functional_test_case.php b/tests/test_framework/phpbb_functional_test_case.php
index 815312e236..a90008c22e 100644
--- a/tests/test_framework/phpbb_functional_test_case.php
+++ b/tests/test_framework/phpbb_functional_test_case.php
@@ -256,6 +256,12 @@ class phpbb_functional_test_case extends phpbb_test_case
 		$phpbb_dispatcher = new phpbb_mock_event_dispatcher();
 		$container->set('migrator', $migrator);
 		$container->set('dispatcher', $phpbb_dispatcher);
+		$cache = $this->getMockBuilder('\phpbb\cache\service')
+			->setConstructorArgs([$this->get_cache_driver(), $config, $this->db, $phpbb_dispatcher, $phpbb_root_path, $phpEx])
+			->setMethods(['deferred_purge'])
+			->getMock();
+		$cache->method('deferred_purge')
+			->willReturnCallback([$cache, 'purge']);
 
 		$extension_manager = new \phpbb\extension\manager(
 			$container,
@@ -265,7 +271,7 @@ class phpbb_functional_test_case extends phpbb_test_case
 			self::$config['table_prefix'] . 'ext',
 			__DIR__ . '/',
 			$phpEx,
-			new \phpbb\cache\service($this->get_cache_driver(), $config, $this->db, $phpbb_dispatcher, $phpbb_root_path, $phpEx)
+			$cache
 		);
 
 		return $extension_manager;