add dependencies for per-file testing (#67)

diff --git a/test/addTarget.js b/test/addTarget.js
index 6f0c85f..f2923b7 100644
--- a/test/addTarget.js
+++ b/test/addTarget.js
@@ -18,6 +18,7 @@
 var fullProject = require('./fixtures/full-project')
     fullProjectStr = JSON.stringify(fullProject),
     pbx = require('../lib/pbxProject'),
+    pbxFile = require('../lib/pbxFile'),
     proj = new pbx('.');
 
 function cleanHash() {