From 4c49974be21dab8253d5c2de1e8bdea4014dd8af Mon Sep 17 00:00:00 2001
From: Nate Moore <git@natemoo.re>
Date: Thu, 4 Jun 2026 00:33:04 -0500
Subject: [PATCH] test: failing repro for string-width

---
 test/string-width.test.ts | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 test/string-width.test.ts

diff --git a/test/string-width.test.ts b/test/string-width.test.ts
new file mode 100644
index 0000000..2f7beb3
--- /dev/null
+++ b/test/string-width.test.ts
@@ -0,0 +1,37 @@
+import { describe, expect, it } from "./suite.ts";
+import * as mod from "../mod.ts";
+
+// stringWidth/charWidth are not exported yet. Cast keeps this type-checking
+// (the cast makes them `any`) while the runtime values are `undefined` today,
+// so calling them throws -> the assertions below fail at runtime, not compile.
+let charWidth = (mod as Record<string, unknown>).charWidth as (
+  cp: number,
+) => number;
+let stringWidth = (mod as Record<string, unknown>).stringWidth as (
+  s: string,
+) => number;
+
+describe("display-width helpers", () => {
+  it("charWidth returns terminal cell columns per codepoint", () => {
+    expect(charWidth(0x41)).toBe(1); // 'A' ASCII occupies 1 cell
+    expect(charWidth(0x4f60)).toBe(2); // CJK 你 is wide -> 2 cells
+    expect(charWidth(0x301)).toBe(0); // combining acute (Mn) -> 0 cells
+    expect(charWidth(0x07)).toBe(0); // BEL control clamped to 0, not -1
+  });
+
+  it("stringWidth sums per-codepoint display width", () => {
+    expect(stringWidth("hello")).toBe(5); // 5 ASCII cells
+    expect(stringWidth("你好")).toBe(4); // two wide CJK -> 4 cells
+    expect(stringWidth("🍔")).toBe(2); // astral emoji is wide -> 2 cells
+  });
+
+  it("stringWidth ignores zero-width combining marks", () => {
+    // decomposed: 'e' (U+0065) + combining acute (U+0301), not precomposed U+00E9
+    expect(stringWidth("é")).toBe(1); // 1 (e) + 0 (mark) = 1 cell
+  });
+
+  it("stringWidth treats a VS16 emoji cluster as 2 cells", () => {
+    // U+2764 (1) + U+FE0F (0): VS16 promotes the cluster to emoji width
+    expect(stringWidth("❤️")).toBe(2);
+  });
+});
-- 
2.51.2