Several improvements

test/format-duration.test.js

@@ -0,0 +1,15 @@
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const formatDuration = require("../lib/format-duration");
+
+test("formats Cookbook ISO 8601 durations for people", () => {
+  assert.equal(formatDuration("PT0H10M0S"), "10 min");
+  assert.equal(formatDuration("PT1H30M0S"), "1 hr 30 min");
+  assert.equal(formatDuration("P2DT1H"), "2 days 1 hr");
+  assert.equal(formatDuration("PT0S"), "0 min");
+});
+
+test("preserves duration values it does not recognize", () => {
+  assert.equal(formatDuration("about an hour"), "about an hour");
+  assert.equal(formatDuration(null), null);
+});