POC of using Happo for visual diff testing

.happo.js

@@ -0,0 +1,18 @@
+const { RemoteBrowserTarget } = require('happo.io');
+
+module.exports = {
+  project: "sphinx_rtd_theme",
+
+  apiKey: process.env.HAPPO_API_KEY,
+  apiSecret: process.env.HAPPO_API_SECRET,
+
+  pages: [
+    { url: 'https://readthedocs-static-dev.s3.us-east-2.amazonaws.com/qa/theme/sphinx4-theme1-docutils17-html5/demo/demo.html', title: 'Sphinx 4, HTML 5' },
+  ],
+
+  targets: {
+    'chrome-desktop': new RemoteBrowserTarget('chrome', {
+      viewport: '1024x768',
+    }),
+  },
+};

package.json

@@ -5,7 +5,8 @@
   "scripts": {
     "dev": "webpack-dev-server --open --config webpack.dev.js",
     "build": "webpack --config webpack.prod.js",
-    "preinstall": "bin/preinstall.js"
+    "preinstall": "bin/preinstall.js",
+    "happo": "happo"
   },
   "repository": {
     "type": "git",
@@ -17,7 +18,9 @@
     "url": "https://github.com/readthedocs/sphinx_rtd_theme/issues"
   },
   "homepage": "https://github.com/readthedocs/sphinx_rtd_theme",
-  "dependencies": {},
+  "dependencies": {
+    "happo.io": "^6.7.0"
+  },
   "devDependencies": {
     "bourbon": "~4.3",
     "bourbon-neat": "~1.9",