Add mock helpers for Range and Selection

To add the text from an element to the clipboard
you need to:
1. get the current Selection
1. create a Range from the contents of the element
2. clear any existing Ranges from the Selection
   and add the new Range to the selection
3. execute the 'copy' command

To track calls to all the DOM APIs involved in
this we need mocks for Range and Selection.

Range:

https://developer.mozilla.org/en-US/docs/Web/API/Range

Selection:

https://developer.mozilla.org/en-US/docs/Web/API/Selection

Also includes a base class to help building out
Web API interface mocks.

tests/javascripts/support/helpers.js

@@ -227,6 +227,50 @@ class WindowMock {
   }
 }
 
+// Base class for mocking an DOM APi interfaces not in JSDOM
+class DOMInterfaceMock {
+
+  constructor (jest, spec) {
+
+    // set up methods so their calls can be tracked
+    // leave implementation/return values to the test
+    spec.methods.forEach(method => this[method] = jest.fn(() => {}));
+
+    // set up props
+    // any spies should be relative to the test so not set here
+    spec.props.forEach(prop => {
+
+      Object.defineProperty(this, prop, {
+        get: () => this[prop],
+        set: value => this[prop] = value
+      });
+
+    });
+
+  }
+
+}
+
+// Very basic class for stubbing the Range interface
+// Only contains methods required for current tests
+class RangeMock extends DOMInterfaceMock {
+
+  constructor (jest) {
+    super(jest, { props: [], methods: ['selectNodeContents'] });
+  }
+
+}
+
+// Very basic class for stubbing the Selection interface
+// Only contains methods required for current tests
+class SelectionMock extends DOMInterfaceMock {
+
+  constructor (jest) {
+    super(jest, { props: [], methods: ['removeAllRanges', 'addRange'] });
+  }
+
+}
+
 // function to ask certain questions of a DOM Element
 const element = function (el) {
   return new ElementQuery(el);
@@ -236,5 +280,7 @@ exports.triggerEvent = triggerEvent;
 exports.clickElementWithMouse = clickElementWithMouse;
 exports.moveSelectionToRadio = moveSelectionToRadio;
 exports.activateRadioWithSpace = activateRadioWithSpace;
+exports.RangeMock = RangeMock;
+exports.SelectionMock = SelectionMock;
 exports.element = element;
 exports.WindowMock = WindowMock;