Restart wheel coast timing and respond immediately on reversal

1 files changed, 14 insertions, 0 deletions

diff --git a/tools/feed-momentum-test.js b/tools/feed-momentum-test.js
index 9f61667..29e4934 100644
--- a/tools/feed-momentum-test.js
+++ b/tools/feed-momentum-test.js
@@ -57,6 +57,20 @@ try {
   await sleep(60); await notch(-1);
   const brake = await settle();
   check('a reverse turn brakes the coast', brake < 3 * one, brake + 'px');
+  for (const dir of [1, -1]) {
+    await page.evaluate(() => window.scrollTo(0, 2000));
+    await notch(dir); await sleep(60);
+    const first = await page.evaluate((dir) => {
+      const ev = new WheelEvent('wheel', { deltaY: -dir * 100, deltaMode: 0, bubbles: true, cancelable: true });
+      Object.defineProperty(ev, 'wheelDeltaY', { value: dir * 120 });
+      const before = scrollY;
+      document.querySelector('#stand-in p').dispatchEvent(ev);
+      return scrollY - before;
+    }, dir);
+    check('reversal responds immediately with a small step (' + dir + ')', first * dir < 0 && Math.abs(first) <= 16, first + 'px');
+    await settle();
+  }
+
   await top();
   check('a trackpad\'s smooth deltas are the browser\'s', !(await notch(1, true)));
   check('...and a notch right after them too (still a trackpad)', !(await notch(1)));