diff --git a/tests/test-extdiff.out b/tests/test-extdiff.out
--- a/tests/test-extdiff.out
+++ b/tests/test-extdiff.out
@@ -29,3 +29,4 @@ options:
 making snapshot of 1 files from rev e27a2475d60a
 making snapshot of 1 files from rev 5e49ec8d3f05
 diffing a.e27a2475d60a a.5e49ec8d3f05
+diff-like tools yield a non-zero exit code