diff --git a/tests/format_probe.cpp b/tests/format_probe.cpp
new file mode 100644
index 0000000..4d2318d
--- /dev/null
+++ b/tests/format_probe.cpp
@@ -0,0 +1,13 @@
+// Scratch probe -- DO NOT MERGE. Exists only to prove two CI lints fire.
+//
+//   1. the quoted public include below must trip
+//      `lint (source conventions)` -> normalise-include-delimiters (RED)
+//   2. the deliberate mis-formatting must make
+//      `lint (clang-format, changed lines)` report a diff and stay GREEN
+#include "fastfields/core/defines.h"
+
+namespace ff {
+int    scratch_probe( int a,int b ) {
+      if(a>b){return a  ;}
+   return b;}
+}  // namespace ff