diff --git a/test/plantuml-preview-test.el b/test/plantuml-preview-test.el
index 236b7a9..8dd9f44 100644
--- a/test/plantuml-preview-test.el
+++ b/test/plantuml-preview-test.el
@@ -8,12 +8,15 @@
 
 ;;; Code:
 
+(defun assert-preview (puml output)
+  (plantuml-preview-string 42 (read-test-file puml))
+  (sleep-for 2)
+  (should (equal (read-test-file output) (read-preview-buffer))))
+
 (ert-deftest preview-test ()
   (setq-local plantuml-jar-path plantuml-test-jar-path)
   (setq-local plantuml-output-type "utxt")
-  (plantuml-preview-string 42 (read-test-file "a-b.puml"))
-  (sleep-for 2)
-  (should (equal (read-test-file "a-b.txt") (read-preview-buffer))))
+  (assert-preview "a-b.puml" "a-b.txt"))
 
 (provide 'plantuml-mode-preview-test)