add unit testing

test/unit/test.js

@@ -0,0 +1,11 @@
+QUnit.module('ImageEditor');
+
+QUnit.test('should load image', function( assert ) {
+  var done = assert.async();
+  var editor = new ImageEditor('canvas');
+  editor.loadImage('fixtures/dog.jpg', function() {
+    assert.ok(editor.canvas.getImage());
+    done();
+  });
+});
+