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.

1 files changed, 39 insertions, 0 deletions

diff --git a/spec/javascripts/matchers.js b/spec/javascripts/matchers.js
index 0d465510fd3..406527b08a3 100644
--- a/spec/javascripts/matchers.js
+++ b/spec/javascripts/matchers.js
@@ -1,3 +1,5 @@
+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.`,
+        };
+      },
+    };
+  },
 };