Only try to run cases with main.js

rendering/webpack.config.js

@@ -3,7 +3,15 @@ const path = require('path');
 
 const cases = path.join(__dirname, 'cases');
 
-const caseDirs = fs.readdirSync(cases);
+const caseDirs = fs.readdirSync(cases).filter(name => {
+  let exists = true;
+  try {
+    fs.accessSync(path.join(cases, name, 'main.js'));
+  } catch (err) {
+    exists = false;
+  }
+  return exists;
+});
 
 const entry = {};
 caseDirs.forEach(c => {