diff --git a/tests/hghave.py b/tests/hghave.py
--- a/tests/hghave.py
+++ b/tests/hghave.py
@@ -1066,6 +1066,11 @@
     )
 
 
+@check("cargo", "cargo tool")
+def has_cargo():
+    return matchoutput('`rustup which cargo` --version', b'cargo')
+
+
 @check("lzma", "python lzma module")
 def has_lzma():
     try:
diff --git a/tests/test-check-cargo-lock.t b/tests/test-check-cargo-lock.t
new file mode 100644
--- /dev/null
+++ b/tests/test-check-cargo-lock.t
@@ -0,0 +1,11 @@
+#require cargo test-repo
+  $ . "$TESTDIR/helpers-testrepo.sh"
+  $ cd "$TESTDIR"/../rust
+
+Check if Cargo.lock is up-to-date. Will fail with a 101 error code if not.
+
+  $ cargo check --locked --all --quiet
+
+However most CIs will run `cargo build` or similar before running the tests, so we need to check if it was modified
+
+  $ testrepohg diff