diff --git a/tests/format.test.ts b/tests/format.test.ts
new file mode 100644
index 0000000..97e1e1c
--- /dev/null
+++ b/tests/format.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+import { truncate } from "../src/tui/lib/format.js";
+
+describe("truncate", () => {
+  it("returns the original string if it is shorter than the limit", () => {
+    expect(truncate("hello", 10)).toBe("hello");
+  });
+
+  it("returns the original string if its length is exactly the limit", () => {
+    expect(truncate("hello", 5)).toBe("hello");
+  });
+
+  it("truncates and appends an ellipsis if the string is longer than the limit", () => {
+    expect(truncate("hello world", 5)).toBe("hell…");
+    expect(truncate("hello world", 8)).toBe("hello w…");
+  });
+
+  it("handles empty strings correctly", () => {
+    expect(truncate("", 5)).toBe("");
+    expect(truncate("", 0)).toBe("");
+  });
+
+  it("handles limit of 0 correctly", () => {
+    expect(truncate("hello", 0)).toBe("…");
+  });
+
+  it("handles limit of 1 correctly", () => {
+    expect(truncate("hello", 1)).toBe("…");
+  });
+
+  it("handles negative limits correctly", () => {
+    expect(truncate("hello", -5)).toBe("…");
+  });
+});