'use strict';

const fs = require('fs');

module.exports = fs.readdirSync(__dirname)
  .filter((filename) => filename !== 'versions.js')
  .map((filename) => filename.slice(0, filename.length - 3)); // remove ".js"

@@ -39,21 +39,21 @@
 );%0A%0A
-module.export
+const version
 s = 
@@ -208,8 +208,127 @@
 e %22.js%22%0A
+%0Aif (process.env.TEST_ONE_REACT_ONLY) %7B%0A  module.exports = versions.slice(-1);%0A%7D else %7B%0A  module.exports = versions;%0A%7D%0A

Add an env var that allows testing only one React version.