diff --git a/tests/checks/ZZ-scratch-red.sh b/tests/checks/ZZ-scratch-red.sh
new file mode 100644
index 0000000..b39cdcb
--- /dev/null
+++ b/tests/checks/ZZ-scratch-red.sh
@@ -0,0 +1,2 @@
+# Scratch branch for PROOF-P0-S3. Never merge. It holds one check that must fail, to show the suite check turns red.
+fail "deliberate failure on a scratch branch (PROOF-P0-S3): the suite check must turn red"