Make test harness asynchronous and run tests natively in Node v0.11.

Closes #1.

test/run.js

@@ -1,35 +1,89 @@
 var fs = require("fs");
 var path = require("path");
+var semver = require("semver");
 var spawn = require("child_process").spawn;
 var recast = require("recast");
 var regenerate = require("../main");
 
-function convert(es6File, es5File) {
-  var es6 = fs.readFileSync(es6File, "utf-8");
-  var tabWidth = require("../lib/util").guessTabWidth(es6);
-  var options = { tabWidth: tabWidth };
-  var ast = recast.parse(es6, options);
-  var es5 = recast.print(regenerate.transform(ast), options);
-  fs.writeFileSync(es5File, es5);
-}
+function convert(es6File, es5File, callback) {
+  fs.readFile(es6File, "utf-8", function(err, es6) {
+    if (err) {
+      return callback(err);
+    }
+
+    var tabWidth = require("../lib/util").guessTabWidth(es6);
+    var options = { tabWidth: tabWidth };
+    var ast = recast.parse(es6, options);
+    var es5 = recast.print(regenerate.transform(ast), options);
 
-convert("test/tests.es6.js", "test/tests.es5.js");
+    fs.writeFile(es5File, es5, callback);
+  });
+}
 
-function bundle(es5File, browserFile) {
+function bundle(es5File, browserFile, callback) {
   var browserify = require("browserify");
   var b = browserify();
   b.add(es5File);
   b.bundle(function(err, src) {
-    if (err) throw err;
-    fs.writeFileSync(browserFile, src);
+    if (err) {
+      return callback(err);
+    }
+    fs.writeFile(browserFile, src, callback);
   });
 }
 
-bundle("./test/tests.es5.js", "test/tests.browser.js");
+var queue = [];
+function enqueue(cmd, args) {
+  queue.push({
+    cmd: cmd,
+    args: args
+  });
+}
+
+function flush() {
+  var entry = queue.shift();
+  if (entry) {
+    var cmd = entry.cmd;
+    if (typeof cmd === "function") {
+      cmd.apply(null, entry.args.concat(asyncCallback));
+    } else {
+      spawn(cmd, entry.args, {
+        stdio: "inherit"
+      }).on("exit", asyncCallback);
+    }
+  }
+}
+
+function asyncCallback(err) {
+  if (err) {
+    console.error("process exited abnormally:", err);
+    process.exit(typeof err === "number" ? err : -1);
+  } else {
+    process.nextTick(flush);
+  }
+}
+
+enqueue(convert, [
+  "test/tests.es6.js",
+  "test/tests.es5.js"
+]);
+
+if (semver.gte(process.version, "0.11.0")) {
+  enqueue("mocha", [
+    "--harmony-generators",
+    "--reporter", "spec",
+    "test/tests.es6.js"
+  ]);
+}
 
-spawn("mocha", [
+enqueue("mocha", [
   "--reporter", "spec",
   "test/tests.es5.js"
-], {
-  stdio: "inherit"
-});
+]);
+
+enqueue(bundle, [
+  "./test/tests.es5.js",
+  "test/tests.browser.js"
+]);
+
+flush();