Validate base64 payload somewhat

package.json

@@ -22,7 +22,8 @@
     "es6-module-loader": "0.14.0",
     "mocha": "~2.0.0",
     "chai": "^1.10.0",
-    "react-tools": "^0.12.1"
+    "react-tools": "^0.12.1",
+    "atob": "^1.1.2"
   },
   "repository": {
     "type": "git",

test/unit-tests.js

@@ -1,6 +1,7 @@
 var fs = require('fs');
 var Builder = require('../index');
 var assert = require('chai').assert;
+var atob = require('atob');
 
 var err = function(e) {
   setTimeout(function() {
@@ -64,7 +65,10 @@ describe('Source Maps', function() {
       var commentPrefix = /^\/\/# sourceMappingURL=data:application\/json;base64,/;
       assert(lastLine.match(commentPrefix));
       var encoding = lastLine.replace(commentPrefix, "");
-      // would be nice to decode here and validate that it's a sourcemap
+      var decoded = JSON.parse(atob(encoding));
+      // not a regular array so tedious
+      assert.equal(1, decoded.sources.length);
+      assert.equal('tree/amd-2.js', decoded.sources[0]);
       done();
     });
   });