feat(util): add object property assert with throw

src/util/index.js

@@ -0,0 +1,13 @@
+function checkDep (obj, propName) {
+  if (!obj) {
+    throw new Error('Object cannot be undefined');
+  }
+
+  if(!obj[propName]) {
+    throw new Error(propName + ' cannot be undefined');
+  }
+
+  return obj[propName];
+};
+
+module.exports.checkDep = checkDep;

src/util/index.spec.js

@@ -0,0 +1,45 @@
+var expect = require('chai').expect;
+
+describe('graffiti util', function() {
+
+  var util = require('./');
+
+  describe('#checkDep', function() {
+
+    it('throws if first argument is undefined', function() {
+
+      try {
+        util.checkDep()
+      } catch (ex) {
+        expect(ex.message).to.eql('Object cannot be undefined');
+        return;
+      }
+
+      throw new Error('Error should have been thrown');
+    });
+
+    it('throws property does not exists', function() {
+
+      try {
+        util.checkDep({}, 'colour');
+      } catch (ex) {
+        expect(ex.message).to.eql('colour cannot be undefined');
+        return;
+      }
+
+      throw new Error('Error should have been thrown');
+    });
+
+    it('returns the property', function () {
+
+      var prop = util.checkDep({
+        colour: 'red'
+      }, 'colour');
+
+      expect(prop).to.eql('red');
+
+    });
+
+  });
+
+});