update constructor, add option validation tests

package.json

@@ -21,5 +21,8 @@
     "expect.js": "~0.3.1",
     "mocha": "~2.4.5",
     "sinon": "~1.17.3"
+  },
+  "dependencies": {
+    "joi": "~8.0.5"
   }
 }