Adds promisify test

src/bin/helper/test/promisify.js

@@ -0,0 +1,24 @@
+import test from 'ava';
+import promisify from '../promisify';
+
+test('should return a fullfilled promise', t => {
+  const callbackFunction = function(cb) {
+    cb();
+  };
+
+  return t.notThrows(promisify(callbackFunction)());
+});
+
+test('should return a rejected promise', async t => {
+  const callbackFunction = function(cb) {
+    cb(new Error());
+  };
+
+  await t.throws(promisify(callbackFunction)());
+
+  const throwFunction = function(cb) {
+    throw new Error('Error');
+  };
+
+  return t.throws(promisify(throwFunction)());
+});