Move window mock functions into helper class

tests/javascripts/support/helpers.js

@@ -75,6 +75,66 @@ class ElementQuery {
   }
 };
 
+class WindowMock {
+  constructor (jest) {
+    this._defaults = {
+      height: window.innerHeight,
+      width: window.innerWidth
+    };
+    this._spies = {
+      document: {}
+    };
+    this._jest = jest;
+  }
+
+  setHeightTo (height) {
+
+    // mock DOM calls for window height
+    window.innerHeight = height;
+    // remove calls to document.documentElement.clientHeight  when jQuery is gone. It's called to support older browsers like IE8
+    this._spies.document.clientHeight = this._jest.spyOn(document.documentElement, 'clientHeight', 'get').mockImplementation(() => height);
+
+  }
+
+  setWidthTo (width) {
+
+    // mock DOM calls for window width
+    window.innerWidth = width;
+    // remove calls to document.documentElement.clientWidth  when jQuery is gone. It's called to support older browsers like IE8
+    this._spies.document.clientWidth = this._jest.spyOn(document.documentElement, 'clientWidth', 'get').mockImplementation(() => height);
+
+  }
+
+  resizeTo (dimensions) {
+
+    this.setHeightTo(dimensions.height);
+    this.setWidthTo(dimensions.width);
+    triggerEvent(window, 'resize');
+
+  }
+
+  scrollBy (scrollPosition) {
+
+    document.documentElement.scrollTop = scrollPosition;
+    triggerEvent(window, 'scroll');
+
+  }
+
+  reset () {
+
+    window.innerHeight = this._defaults.height;
+    window.innerWidth = this._defaults.width;
+    document.documentElement.scrollTop = 0;
+
+    // reset all spies
+    Object.keys(this._spies).forEach(key => {
+      const objectSpies = this._spies[key];
+      Object.keys(objectSpies).forEach(key => objectSpies[key].mockClear());
+    });
+
+  }
+}
+
 // function to ask certain questions of a DOM Element
 const element = function (el) {
   return new ElementQuery(el);
@@ -82,3 +142,4 @@ const element = function (el) {
 
 exports.triggerEvent = triggerEvent;
 exports.element = element;
+exports.WindowMock = WindowMock;