Timeline: repair oldest/newest metrics if we fetch nothing

ts/test-node/util/sleep_test.ts

@@ -0,0 +1,36 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { useFakeTimers } from 'sinon';
+
+import { sleep } from '../../util/sleep';
+
+describe('sleep', () => {
+  beforeEach(function beforeEach() {
+    // This isn't a hook.
+    // eslint-disable-next-line react-hooks/rules-of-hooks
+    this.clock = useFakeTimers();
+  });
+
+  afterEach(function afterEach() {
+    this.clock.restore();
+  });
+
+  it('returns a promise that resolves after the specified number of milliseconds', async function test() {
+    let isDone = false;
+
+    (async () => {
+      await sleep(123);
+      isDone = true;
+    })();
+
+    assert.isFalse(isDone);
+
+    await this.clock.tickAsync(100);
+    assert.isFalse(isDone);
+
+    await this.clock.tickAsync(25);
+    assert.isTrue(isDone);
+  });
+});