fix(accordion): add open class when expanded

- add `open` class to `.panel-collapse` when open.
- fix missing closing `<` on test.

Closes #4152
Fixes #3419

src/accordion/test/accordion.spec.js

@@ -114,7 +114,7 @@ describe('accordion', function () {
     it('should expose the controller on the view', function () {
       $templateCache.put('template/accordion/accordion.html', '<div>{{accordion.text}}</div>');
 
-      element = $compile('<accordion></accordion')(scope);
+      element = $compile('<accordion></accordion>')(scope);
       scope.$digest();
 
       var ctrl = element.controller('accordion');
@@ -211,6 +211,17 @@ describe('accordion', function () {
         scope.$digest();
         expect(findGroupBody(0).scope().isOpen).toBe(false);
       });
+
+      it('should add "open" when opened', function() {
+        var group = groups.eq(0);
+        findGroupLink(0).click();
+        scope.$digest();
+        expect(group).toHaveClass('panel-open');
+
+        findGroupLink(0).click();
+        scope.$digest();
+        expect(group).not.toHaveClass('panel-open');
+      });
     });
 
     describe('with dynamic panels', function () {

template/accordion/accordion-group.html

@@ -1,4 +1,4 @@
-<div class="panel panel-default">
+<div class="panel panel-default" ng-class="{'panel-open': isOpen}">
   <div class="panel-heading">
     <h4 class="panel-title">
       <a href tabindex="0" class="accordion-toggle" ng-click="toggleOpen()" accordion-transclude="heading"><span ng-class="{'text-muted': isDisabled}">{{heading}}</span></a>