test: unit tests for the mailto URL builder

tests/mailto.test.js

@@ -0,0 +1,33 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { buildMailtoUrl } from "../js/mailto.js";
+
+test("builds a plain mailto URL when there is no subject or body", () => {
+  assert.equal(buildMailtoUrl({ to: "ada@example.com" }), "mailto:ada@example.com");
+});
+
+test("includes subject and body as URL-encoded query parameters", () => {
+  const url = buildMailtoUrl({
+    to: "owner@example.com",
+    subject: "Hello, Ada!",
+    body: "Line one\nLine two & <more>",
+  });
+
+  assert.ok(url.startsWith("mailto:owner@example.com?"));
+
+  const params = new URL(url).searchParams;
+  assert.equal(params.get("subject"), "Hello, Ada!");
+  assert.equal(params.get("body"), "Line one\nLine two & <more>");
+});
+
+test("omits empty subject and body", () => {
+  const url = buildMailtoUrl({ to: "owner@example.com", subject: "", body: "" });
+  assert.equal(url, "mailto:owner@example.com");
+});
+
+test("encodes spaces and special characters so the mail client opens pre-filled", () => {
+  const url = buildMailtoUrl({ to: "o@example.com", subject: "a b", body: "x&y=z" });
+  const params = new URL(url).searchParams;
+  assert.equal(params.get("subject"), "a b");
+  assert.equal(params.get("body"), "x&y=z");
+});