feat: add comprehensive end-to-end test suite

e2e/test_vu_meter.ts

@@ -0,0 +1,49 @@
+import { setupTest, startEngine, startClientInTmux, openCmdFifo, wait, ensureGenTone, exec, tmuxCapturePane, teardownTest } from './test_utils';
+import * as globals from "./test_globals";
+
+export async function testVUMeter(): Promise<void> {
+  console.log("\nTest: VU METER RESPONDS TO AUDIO");
+  setupTest();
+  const engine = await startEngine();
+  await startClientInTmux();
+  openCmdFifo();
+  await wait(500);
+
+  // Capture initial VU line (should be empty/spaces)
+  let pane = tmuxCapturePane("looper", "0");
+  const paneLines = pane.split("\n");
+  // Look for any line containing x or # – that is the VU meter line.
+  const vuLineBefore = paneLines.find(l => /[x#]/.test(l)) || "";
+  console.log(`  Initial VU line: "${vuLineBefore.trim()}"`);
+
+  // Generate tone in background (does not block the test)
+  ensureGenTone();
+  const toneProc = exec(`${globals.GEN_TONE_BIN} 3.0 "looper:ch0in"`, { timeout: 8000 });
+
+  // Wait for audio to start reaching the meter
+  await wait(1500);
+
+  // Capture pane while tone is playing
+  pane = tmuxCapturePane("looper", "0");
+  const paneLines2 = pane.split("\n");
+  // Same detection as above
+  const vuLineDuring = paneLines2.find(l => /[x#]/.test(l)) || "";
+  console.log(`  VU line during tone: "${vuLineDuring.trim()}"`);
+
+  // The VU meter should show non-space characters (at least one 'x' or '#')
+  const hasSignal = /[x#]/.test(vuLineDuring);
+  if (hasSignal) {
+    console.log("  PASS: VU meter shows signal (non‑space characters)");
+  } else {
+    console.log("  FAIL: VU meter line does not show any signal characters");
+    console.log("  Pane excerpt:\n" + pane.slice(0, 2000));
+    engine.kill(); teardownTest();
+    throw new Error("VU meter not responsive");
+  }
+
+  // Wait for tone process to finish
+  try { toneProc.kill(); } catch {}
+
+  engine.kill();
+  teardownTest();
+}