Update tests

Re-order tests - when sticking and unsticking.

Add mocks to test that sticking and unsticking works for smaller and
larger screens, test that all three conditions in the checkScroll
function stick/unstick.

spec/unit/stick-at-top-when-scrolling.spec.js

@@ -13,27 +13,109 @@ describe("stick-at-top-when-scrolling", function(){
     $stickyWrapper.remove();
   });
 
-  it('should add fixed class on stick', function(){
-    expect(!$stickyElement.hasClass('content-fixed')).toBe(true);
-    GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
-    expect($stickyElement.hasClass('content-fixed')).toBe(true);
+  describe('when stick is called', function(){
+
+    it('should add fixed class on stick', function(){
+      expect(!$stickyElement.hasClass('content-fixed')).toBe(true);
+      GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
+      expect($stickyElement.hasClass('content-fixed')).toBe(true);
+    });
+
+    it('should insert shim when sticking the element', function(){
+      expect($('.shim').length).toBe(0);
+      GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
+      expect($('.shim').length).toBe(1);
+    });
+
+    it('should insert shim with minimum height', function(){
+      GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
+      expect($('.shim').height()).toBe(1);
+    });
+
   });
 
-  it('should remove fixed class on release', function(){
-    $stickyElement.addClass('content-fixed');
-    GOVUK.stickAtTopWhenScrolling.release($stickyElement);
-    expect(!$stickyElement.hasClass('content-fixed')).toBe(true);
+  describe('when release is called', function(){
+
+    it('should remove fixed class', function(){
+      $stickyElement.addClass('content-fixed');
+      GOVUK.stickAtTopWhenScrolling.release($stickyElement);
+      expect($stickyElement.hasClass('content-fixed')).toBe(false);
+    });
+
+    it('should remove the shim', function(){
+      $stickyElement = $('<div class="stick-at-top-when-scrolling content-fixed"></div>');
+      GOVUK.stickAtTopWhenScrolling.release($stickyElement);
+      expect($('.shim').length).toBe(0);
+    });
+
   });
 
-  it('should insert shim when sticking content', function(){
-    expect($('.shim').length).toBe(0);
-    GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
-    expect($('.shim').length).toBe(1);
+  describe('for larger screens (>768px)', function(){
+
+    beforeEach(function() {
+      GOVUK.stickAtTopWhenScrolling.getWindowPositions = function(){
+        return {
+          scrollTop: 300
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.getElementOffset = function(){
+        return {
+          top: 300
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.getWindowDimensions = function(){
+        return {
+          height: 768,
+          width: 769
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.$els = $stickyElement;
+      GOVUK.stickAtTopWhenScrolling._hasScrolled = true;
+      GOVUK.stickAtTopWhenScrolling.checkScroll();
+    });
+
+    it('should stick, if the scroll position is past the element position', function(){
+      expect($stickyElement.hasClass('content-fixed')).toBe(true);
+    });
+
+    it('should unstick, if the scroll position is less than the point at which scrolling started', function(){
+      GOVUK.stickAtTopWhenScrolling.getWindowPositions = function() {
+        return {
+          scrollTop: 0
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.$els = $stickyElement;
+      GOVUK.stickAtTopWhenScrolling._hasScrolled = true;
+      GOVUK.stickAtTopWhenScrolling.checkScroll();
+      expect($stickyElement.hasClass('content-fixed')).toBe(false);
+    });
+
   });
 
-  it('should insert shim with minimum height', function(){
-    GOVUK.stickAtTopWhenScrolling.stick($stickyElement);
-    expect($('.shim').height()).toBe(1);
+  describe('for smaller screens (<=768px)', function(){
+
+    beforeEach(function() {
+      GOVUK.stickAtTopWhenScrolling.getWindowDimensions = function() {
+        return {
+          height: 768,
+          width: 767
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.getElementOffset = function() {
+        return {
+          top: 300
+        };
+      };
+      GOVUK.stickAtTopWhenScrolling.$els = $stickyElement;
+      GOVUK.stickAtTopWhenScrolling._hasScrolled = true;
+      GOVUK.stickAtTopWhenScrolling.checkScroll();
+    });
+
+    it('should unstick the element', function(){
+      expect($stickyElement.hasClass('content-fixed')).toBe(false);
+    });
+
   });
+
 });