Use Client APIs to resolve URLs (#5148)

webapp/webpack.config.js

@@ -159,6 +159,7 @@ if (TEST) {
     config.entry = ['babel-polyfill', './root.jsx'];
     config.target = 'node';
     config.externals = [nodeExternals()];
+    config.resolve.alias['./client/web_client.jsx'] = path.resolve(__dirname, 'client/test_web_client.jsx');
 } else {
     // For some reason these break mocha. So they go here.
     config.plugins.push(