Add helpers for JS tests

To help with asserting some things which were
repeated in the tests.

tests/javascripts/support/helpers.js

@@ -0,0 +1,84 @@
+const triggerEvent = (el, evtType) => {
+  const evt = new Event(evtType, {
+    bubbles: true,
+    cancelable: true
+  });
+
+  el.dispatchEvent(evt);
+};
+
+class ElementQuery {
+  constructor (el) {
+    this.el = el;
+  }
+  
+  get nodeName () {
+    return this.el.nodeName.toLowerCase();
+  }
+
+  get firstTextNodeValue () {
+    const textNodes = Array.from(this.el.childNodes).filter(el => el.nodeType === 3);
+
+    return textNodes.length ? textNodes[0].nodeValue : undefined;
+  };
+  // returns the elements attributes as an object
+  hasAttributesSetTo (mappings) {
+    if (!this.el.hasAttributes()) { return false; }
+
+    const keys = Object.keys(mappings);
+    let matches = 0;
+
+    keys.forEach(key => {
+      if (this.el.hasAttribute(key) && (this.el.attributes[key].value === mappings[key])) {
+        matches++;
+      }
+    });
+
+    return matches === keys.length;
+  }
+
+  hasClass (classToken) {
+    return Array.from(this.el.classList).includes(classToken);
+  }
+
+  is (state) {
+    const test = `_is${state.charAt(0).toUpperCase()}${state.slice(1)}`;
+
+    if (ElementQuery.prototype.hasOwnProperty(test)) {
+      return this[test]();
+    }
+  }
+
+  // looks for a sibling before the el that matches the supplied test function
+  // the test function gets sent each sibling, wrapped in an Element instance
+  getPreviousSibling (test) {
+    let node = this.el.previousElementSibling;
+    let el;
+
+    while(node) {
+      el = element(node);
+
+      if (test(el)) {
+        return node;
+      }
+
+      node = node.previousElementSibling;
+    }
+
+    return null;
+  }
+
+  _isHidden () {
+    const display = window.getComputedStyle(this.el).getPropertyValue('display');
+
+    return display === 'none';
+  }
+};
+
+// function to ask certain questions of a DOM Element
+const element = function (el) {
+  return new ElementQuery(el);
+};
+
+exports.triggerEvent = triggerEvent;
+exports.element = element;