diff --git a/tests/test-check-cargo-lock.t b/tests/test-check-cargo-lock.t
--- a/tests/test-check-cargo-lock.t
+++ b/tests/test-check-cargo-lock.t
@@ -8,4 +8,4 @@ Check if Cargo.lock is up-to-date. Will 
 
 However most CIs will run `cargo build` or similar before running the tests, so we need to check if it was modified
 
-  $ testrepohg diff
+  $ testrepohg diff Cargo.lock