1 files changed, 89 insertions, 0 deletions
diff --git a/spec/frontend/lib/utils/navigation_utility_spec.js b/spec/frontend/lib/utils/navigation_utility_spec.js
index 88172f38894..6a880a0f354 100644
--- a/spec/frontend/lib/utils/navigation_utility_spec.js
+++ b/spec/frontend/lib/utils/navigation_utility_spec.js
@@ -1,4 +1,5 @@
 import findAndFollowLink from '~/lib/utils/navigation_utility';
+import * as navigationUtils from '~/lib/utils/navigation_utility';
 import { visitUrl } from '~/lib/utils/url_utility';
 
 jest.mock('~/lib/utils/url_utility');
@@ -21,3 +22,91 @@ describe('findAndFollowLink', () => {
     expect(visitUrl).not.toHaveBeenCalled();
   });
 });
+
+describe('prefetchDocument', () => {
+  it('creates a prefetch link tag', () => {
+    const linkElement = document.createElement('link');
+
+    jest.spyOn(document, 'createElement').mockImplementation(() => linkElement);
+    jest.spyOn(document.head, 'appendChild');
+
+    navigationUtils.prefetchDocument('index.htm');
+
+    expect(document.head.appendChild).toHaveBeenCalledWith(linkElement);
+    expect(linkElement.href).toEqual('http://test.host/index.htm');
+    expect(linkElement.rel).toEqual('prefetch');
+    expect(linkElement.getAttribute('as')).toEqual('document');
+  });
+});
+
+describe('initPrefetchLinks', () => {
+  let newLink;
+
+  beforeEach(() => {
+    newLink = document.createElement('a');
+    newLink.href = 'index_prefetch.htm';
+    newLink.classList.add('js-test-prefetch-link');
+    document.body.appendChild(newLink);
+  });
+
+  it('adds to all links mouse out handlers when hovered', () => {
+    const mouseOverEvent = new Event('mouseover');
+
+    jest.spyOn(newLink, 'addEventListener');
+
+    navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+    newLink.dispatchEvent(mouseOverEvent);
+
+    expect(newLink.addEventListener).toHaveBeenCalled();
+  });
+
+  it('it is not fired when less then 100ms over link', () => {
+    const mouseOverEvent = new Event('mouseover');
+    const mouseOutEvent = new Event('mouseout');
+
+    jest.spyOn(newLink, 'addEventListener');
+    jest.spyOn(navigationUtils, 'prefetchDocument').mockImplementation(() => true);
+
+    navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+    newLink.dispatchEvent(mouseOverEvent);
+    newLink.dispatchEvent(mouseOutEvent);
+
+    expect(navigationUtils.prefetchDocument).not.toHaveBeenCalled();
+  });
+
+  describe('executes correctly when hovering long enough', () => {
+    const mouseOverEvent = new Event('mouseover');
+
+    beforeEach(() => {
+      jest.useFakeTimers();
+
+      jest.spyOn(global, 'setTimeout');
+      jest.spyOn(newLink, 'removeEventListener');
+    });
+
+    it('calls prefetchDocument which adds to document', () => {
+      jest.spyOn(document.head, 'appendChild');
+
+      navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+      newLink.dispatchEvent(mouseOverEvent);
+
+      jest.runAllTimers();
+
+      expect(setTimeout).toHaveBeenCalledWith(expect.any(Function), 100);
+      expect(document.head.appendChild).toHaveBeenCalled();
+    });
+
+    it('removes Event Listener when fired so only done once', () => {
+      navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+      newLink.dispatchEvent(mouseOverEvent);
+
+      jest.runAllTimers();
+
+      expect(newLink.removeEventListener).toHaveBeenCalledWith(
+        'mouseover',
+        expect.any(Function),
+        true,
+      );
+    });
+  });
+});