use browserify programmatically

test/browser-runner.js

@@ -1,6 +1,7 @@
 require('colors');
-var childProcess = require('child_process');
+var browserify = require('browserify');
 var EventEmitter = require('events').EventEmitter;
+var fs = require('fs');
 var httpServer = require('http-server');
 var nodeunit = require('nodeunit');
 var optimist = require('./runner-options');
@@ -128,17 +129,10 @@ function run() {
 }
 
 // browserify and run the tests
-childProcess.exec(
-  'node_modules/browserify/bin/cmd.js test/worker.js -o test/worker-bundle.js',
-  function (err, stdout, stderr) {
-    if (err) {
-      console.log(stdout.toString());
-      console.log('Failed to browserify test/worker');
-      console.log(err);
-      process.exit(1);
-      return;
-    }
-
+browserify('./test/worker.js').
+  bundle().
+  pipe(fs.createWriteStream('./test/worker-bundle.js')).
+  on('finish', function () {
     // start web server
     var webServer = httpServer.createServer().listen(httpPort);