Make favicon tests more fault resistent

It seems like every new version of Chrome renders the favicon canvas
differently. This reduces the problems with it by creating a more fault
tolerant check, which compares the color values in the pixels and is
okay if they are within a certain threshold.

package.json

@@ -161,6 +161,7 @@
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^4.0.0-beta.0",
     "nodemon": "^1.18.4",
+    "pixelmatch": "^4.0.2",
     "prettier": "1.15.3",
     "vue-jest": "^3.0.2",
     "webpack-dev-server": "^3.1.14",

spec/javascripts/lib/utils/common_utils_spec.js

@@ -3,6 +3,25 @@ import * as commonUtils from '~/lib/utils/common_utils';
 import MockAdapter from 'axios-mock-adapter';
 import { faviconDataUrl, overlayDataUrl, faviconWithOverlayDataUrl } from './mock_data';
 
+const PIXEL_TOLERANCE = 0.2;
+
+/**
+ * Loads a data URL as the src of an
+ * {@link https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/Image|Image}
+ * and resolves to that Image once loaded.
+ *
+ * @param url
+ * @returns {Promise}
+ */
+const urlToImage = url =>
+  new Promise(resolve => {
+    const img = new Image();
+    img.onload = function() {
+      resolve(img);
+    };
+    img.src = url;
+  });
+
 describe('common_utils', () => {
   describe('parseUrl', () => {
     it('returns an anchor tag with url', () => {
@@ -513,8 +532,9 @@ describe('common_utils', () => {
     it('should return the favicon with the overlay', done => {
       commonUtils
         .createOverlayIcon(faviconDataUrl, overlayDataUrl)
-        .then(url => {
-          expect(url).toEqual(faviconWithOverlayDataUrl);
+        .then(url => Promise.all([urlToImage(url), urlToImage(faviconWithOverlayDataUrl)]))
+        .then(([actual, expected]) => {
+          expect(actual).toImageDiffEqual(expected, PIXEL_TOLERANCE);
           done();
         })
         .catch(done.fail);
@@ -536,10 +556,10 @@ describe('common_utils', () => {
     it('should set page favicon to provided favicon overlay', done => {
       commonUtils
         .setFaviconOverlay(overlayDataUrl)
-        .then(() => {
-          expect(document.getElementById('favicon').getAttribute('href')).toEqual(
-            faviconWithOverlayDataUrl,
-          );
+        .then(() => document.getElementById('favicon').getAttribute('href'))
+        .then(url => Promise.all([urlToImage(url), urlToImage(faviconWithOverlayDataUrl)]))
+        .then(([actual, expected]) => {
+          expect(actual).toImageDiffEqual(expected, PIXEL_TOLERANCE);
           done();
         })
         .catch(done.fail);
@@ -582,10 +602,10 @@ describe('common_utils', () => {
 
       commonUtils
         .setCiStatusFavicon(BUILD_URL)
-        .then(() => {
-          const favicon = document.getElementById('favicon');
-
-          expect(favicon.getAttribute('href')).toEqual(faviconWithOverlayDataUrl);
+        .then(() => document.getElementById('favicon').getAttribute('href'))
+        .then(url => Promise.all([urlToImage(url), urlToImage(faviconWithOverlayDataUrl)]))
+        .then(([actual, expected]) => {
+          expect(actual).toImageDiffEqual(expected, PIXEL_TOLERANCE);
           done();
         })
         .catch(done.fail);

spec/javascripts/matchers.js

+import pixelmatch from 'pixelmatch';
+
 export default {
   toContainText: () => ({
     compare(vm, text) {
@@ -54,4 +56,41 @@ export default {
       return result;
     },
   }),
+  toImageDiffEqual: () => {
+    const getImageData = img => {
+      const canvas = document.createElement('canvas');
+      canvas.width = img.width;
+      canvas.height = img.height;
+      canvas.getContext('2d').drawImage(img, 0, 0);
+      return canvas.getContext('2d').getImageData(0, 0, img.width, img.height).data;
+    };
+
+    return {
+      compare(actual, expected, threshold = 0.1) {
+        if (actual.height !== expected.height || actual.width !== expected.width) {
+          return {
+            pass: false,
+            message: `Expected image dimensions (h x w) of ${expected.height}x${expected.width}.
+            Received an image with ${actual.height}x${actual.width}`,
+          };
+        }
+
+        const { width, height } = actual;
+        const differentPixels = pixelmatch(
+          getImageData(actual),
+          getImageData(expected),
+          null,
+          width,
+          height,
+          { threshold },
+        );
+
+        return {
+          pass: differentPixels < 20,
+          message: `${differentPixels} pixels differ more than ${threshold *
+            100} percent between input and output.`,
+        };
+      },
+    };
+  },
 };

yarn.lock

@@ -7735,6 +7735,13 @@ pinkie@^2.0.0:
   resolved "https://registry.yarnpkg.com/pinkie/-/pinkie-2.0.4.tgz#72556b80cfa0d48a974e80e77248e80ed4f7f870"
   integrity sha1-clVrgM+g1IqXToDnckjoDtT3+HA=
 
+pixelmatch@^4.0.2:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/pixelmatch/-/pixelmatch-4.0.2.tgz#8f47dcec5011b477b67db03c243bc1f3085e8854"
+  integrity sha1-j0fc7FARtHe2fbA8JDvB8wheiFQ=
+  dependencies:
+    pngjs "^3.0.0"
+
 pkg-dir@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/pkg-dir/-/pkg-dir-1.0.0.tgz#7a4b508a8d5bb2d629d447056ff4e9c9314cf3d4"
@@ -7766,6 +7773,11 @@ pn@^1.1.0:
   resolved "https://registry.yarnpkg.com/pn/-/pn-1.1.0.tgz#e2f4cef0e219f463c179ab37463e4e1ecdccbafb"
   integrity sha512-2qHaIQr2VLRFoxe2nASzsV6ef4yOOH+Fi9FBOVH6cqeSgUnoyySPZkxzLuzd+RYOQTRpROA0ztTMqxROKSb/nA==
 
+pngjs@^3.0.0:
+  version "3.3.3"
+  resolved "https://registry.yarnpkg.com/pngjs/-/pngjs-3.3.3.tgz#85173703bde3edac8998757b96e5821d0966a21b"
+  integrity sha512-1n3Z4p3IOxArEs1VRXnZ/RXdfEniAUS9jb68g58FIXMNkPJeZd+Qh4Uq7/e0LVxAQGos1eIUrqrt4FpjdnEd+Q==
+
 pofile@^1:
   version "1.0.11"
   resolved "https://registry.yarnpkg.com/pofile/-/pofile-1.0.11.tgz#35aff58c17491d127a07336d5522ebc9df57c954"