improve structure & switch to yarn

config/jest-test-server.loader.js

@@ -0,0 +1,10 @@
+const path = require('path');
+const jestPuppeteerConfig = require('../jest-puppeteer.config.base');
+
+module.exports = {
+  process: (src, filePath, config) => {
+    const deploymentPath = path.relative(path.dirname(config.globals.baseConfig), filePath);
+    const split = deploymentPath.split(path.sep);
+    return `module.exports = ${JSON.stringify(`http://localhost:${jestPuppeteerConfig.server.port}/${path.posix.join(...split)}`)}`;
+  },
+};