refactor app directory structure and add tests

tests/node_modules/nightwatch/lib/api/assertions/elementPresent.js

@@ -0,0 +1,34 @@
+/**
+ * Checks if the given element exists in the DOM.
+ *
+ * ```
+ *    this.demoTest = function (client) {
+ *      browser.assert.elementPresent("#main");
+ *    };
+ * ```
+ *
+ * @method elementPresent
+ * @param {string} selector The selector (CSS / Xpath) used to locate the element.
+ * @param {string} [message] Optional log message to display in the output. If missing, one is displayed by default.
+ * @api assertions
+ */
+
+var util = require('util');
+exports.assertion = function(selector, msg) {
+
+  this.message = msg || util.format('Testing if element <%s> is present.', selector);
+  this.expected = 'present';
+
+  this.pass = function(value) {
+    return value == 'present';
+  };
+
+  this.value = function(result) {
+    return (result.status !== 0 || result.value.length === 0) ? 'not present' : 'present';
+  };
+
+  this.command = function(callback) {
+    return this.api.elements(this.client.locateStrategy, selector, callback);
+  };
+
+};