Copy missing test in date_picker_spec.js from CE

spec/javascripts/vue_shared/components/sidebar/date_picker_spec.js

@@ -12,6 +12,15 @@ describe('sidebarDatePicker', () => {
     });
   });
 
+  it('should emit toggleCollapse when collapsed toggle sidebar is clicked', () => {
+    const toggleCollapse = jasmine.createSpy();
+    vm.$on('toggleCollapse', toggleCollapse);
+
+    vm.$el.querySelector('.issuable-sidebar-header .gutter-toggle').click();
+
+    expect(toggleCollapse).toHaveBeenCalled();
+  });
+
   it('should render collapsed-calendar-icon', () => {
     expect(vm.$el.querySelector('.sidebar-collapsed-icon')).toBeDefined();
   });