From f46c36ed976abd05be52be5cc980ccbd9e9265f3 Mon Sep 17 00:00:00 2001
From: Brian Ambielli <bambielli@flexport.com>
Date: Fri, 17 May 2019 09:18:52 -0500
Subject: [PATCH] fixes #8256

---
 src/ui/handler/scroll_zoom.js            |  9 ++-
 test/README.md                           |  3 +-
 test/unit/ui/handler/scroll_zoom.test.js | 89 ++++++++++++++++++++++++
 3 files changed, 97 insertions(+), 4 deletions(-)

diff --git a/src/ui/handler/scroll_zoom.js b/src/ui/handler/scroll_zoom.js
index 3f018c748eb..eab8bbf8556 100644
--- a/src/ui/handler/scroll_zoom.js
+++ b/src/ui/handler/scroll_zoom.js
@@ -215,9 +215,12 @@ class ScrollZoomHandler {
         }
 
         this._active = true;
-        this._zooming = true;
-        this._map.fire(new Event('movestart', {originalEvent: e}));
-        this._map.fire(new Event('zoomstart', {originalEvent: e}));
+        if (!this.isZooming()) {
+            this._zooming = true;
+            this._map.fire(new Event('movestart', {originalEvent: e}));
+            this._map.fire(new Event('zoomstart', {originalEvent: e}));
+        }
+
         if (this._finishTimeout) {
             clearTimeout(this._finishTimeout);
         }
diff --git a/test/README.md b/test/README.md
index ed53f9218df..79dcfe71133 100644
--- a/test/README.md
+++ b/test/README.md
@@ -12,7 +12,8 @@ There are two test suites associated with Mapbox GL JS
 
  To run individual tests:
 
- - Unit tests: `yarn test-unit path/to/file.test.js` where the path begins within the `/test/unit/` directory
+ - Unit tests: `yarn test-unit path/to/file.test.js` where path *does not include* `test/unit/` 
+   - e.g. `yarn test-unit ui/handler/scroll_zoom.test.js`
  - Render tests: `yarn test-render render-test-name` (e.g. `yarn test-render background-color/default`)
 
 ## Writing Unit Tests
diff --git a/test/unit/ui/handler/scroll_zoom.test.js b/test/unit/ui/handler/scroll_zoom.test.js
index 6cecaf7551f..21177f00505 100644
--- a/test/unit/ui/handler/scroll_zoom.test.js
+++ b/test/unit/ui/handler/scroll_zoom.test.js
@@ -4,6 +4,7 @@ import window from '../../../../src/util/window';
 import Map from '../../../../src/ui/map';
 import DOM from '../../../../src/util/dom';
 import simulate from 'mapbox-gl-js-test/simulate_interaction';
+import sinon from 'sinon';
 
 function createMap(t) {
     t.stub(Map.prototype, '_detectMissingCSS');
@@ -148,5 +149,93 @@ test('ScrollZoomHandler', (t) => {
         t.end();
     });
 
+    t.test('emits one movestart event and one moveend event while zooming', (t) => {
+        const clock = sinon.useFakeTimers(now);
+        const map = createMap(t);
+
+        let startCount = 0;
+        map.on('movestart', () => {
+            startCount += 1;
+        });
+
+        let endCount = 0;
+        map.on('moveend', () => {
+            endCount += 1;
+        });
+
+        const events = [
+            [2, {type: 'trackpad', deltaY: -1}],
+            [7, {type: 'trackpad', deltaY: -2}],
+            [30, {type: 'wheel', deltaY: -5}]
+        ];
+
+        const end = now + 50;
+        let lastWheelEvent = now;
+
+        while (now++ < end) {
+            if (events.length && lastWheelEvent + events[0][0] === now) {
+                const [, event] = events.shift();
+                simulate.wheel(map.getCanvas(), event);
+                lastWheelEvent = now;
+            }
+            if (now % 20 === 0) {
+                map._renderTaskQueue.run();
+            }
+        }
+
+        clock.tick(200);
+
+        t.equal(startCount, 1);
+        t.equal(endCount, 1);
+
+        clock.restore();
+
+        t.end();
+    });
+
+    t.test('emits one zoomstart event and one zoomend event while zooming', (t) => {
+        const clock = sinon.useFakeTimers(now);
+        const map = createMap(t);
+
+        let startCount = 0;
+        map.on('zoomstart', () => {
+            startCount += 1;
+        });
+
+        let endCount = 0;
+        map.on('zoomend', () => {
+            endCount += 1;
+        });
+
+        const events = [
+            [2, {type: 'trackpad', deltaY: -1}],
+            [7, {type: 'trackpad', deltaY: -2}],
+            [30, {type: 'wheel', deltaY: -5}],
+        ];
+
+        const end = now + 50;
+        let lastWheelEvent = now;
+
+        while (now++ < end) {
+            if (events.length && lastWheelEvent + events[0][0] === now) {
+                const [, event] = events.shift();
+                simulate.wheel(map.getCanvas(), event);
+                lastWheelEvent = now;
+            }
+            if (now % 20 === 0) {
+                map._renderTaskQueue.run();
+            }
+        }
+
+        clock.tick(200);
+
+        t.equal(startCount, 1);
+        t.equal(endCount, 1);
+
+        clock.restore();
+
+        t.end();
+    });
+
     t.end();
 });