feat(render): add output speed display (#110)

tests/speed-tracker.test.js

@@ -0,0 +1,57 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdtemp, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { getOutputSpeed } from '../dist/speed-tracker.js';
+
+async function createTempHome() {
+  return await mkdtemp(path.join(tmpdir(), 'claude-hud-speed-'));
+}
+
+test('getOutputSpeed returns null when output tokens are missing', () => {
+  const speed = getOutputSpeed({ context_window: { current_usage: { input_tokens: 10 } } });
+  assert.equal(speed, null);
+});
+
+test('getOutputSpeed computes tokens per second within window', async () => {
+  const tempHome = await createTempHome();
+
+  try {
+    const base = { homeDir: () => tempHome };
+    const first = getOutputSpeed(
+      { context_window: { current_usage: { output_tokens: 10 } } },
+      { ...base, now: () => 1000 }
+    );
+    assert.equal(first, null);
+
+    const second = getOutputSpeed(
+      { context_window: { current_usage: { output_tokens: 20 } } },
+      { ...base, now: () => 1500 }
+    );
+    assert.ok(second !== null);
+    assert.ok(Math.abs(second - 20) < 0.01);
+  } finally {
+    await rm(tempHome, { recursive: true, force: true });
+  }
+});
+
+test('getOutputSpeed ignores stale windows', async () => {
+  const tempHome = await createTempHome();
+
+  try {
+    const base = { homeDir: () => tempHome };
+    getOutputSpeed(
+      { context_window: { current_usage: { output_tokens: 10 } } },
+      { ...base, now: () => 1000 }
+    );
+
+    const speed = getOutputSpeed(
+      { context_window: { current_usage: { output_tokens: 30 } } },
+      { ...base, now: () => 8000 }
+    );
+    assert.equal(speed, null);
+  } finally {
+    await rm(tempHome, { recursive: true, force: true });
+  }
+});