1 files changed, 16 insertions, 0 deletions
diff --git a/src/features/layout/logic/marker.test.ts b/src/features/layout/logic/marker.test.ts
new file mode 100644
index 0000000..d9e3826
--- /dev/null
+++ b/src/features/layout/logic/marker.test.ts
@@ -0,0 +1,16 @@
+import { describe, expect, it } from "vitest";
+import { markerOutline } from "./marker";
+
+describe("markerOutline — the diagnostic tile-border mapping", () => {
+  it("main → a 4px solid red outline (the main tile's marker)", () => {
+    expect(markerOutline("main")).toBe("4px solid red");
+  });
+
+  it("side → a 4px solid green outline (the side tile's marker)", () => {
+    expect(markerOutline("side")).toBe("4px solid green");
+  });
+
+  it("no marker → no outline (existing trees render exactly as before)", () => {
+    expect(markerOutline(undefined)).toBeUndefined();
+  });
+});