Ember component with optional block

component_with_optional_block.handlebars

<!-- app/templates/*.hbs -->
{{#if template}}
  {{yield}}
{{else}}
  {{defaultContent}}
{{/if}}

testing_component_with_optional_block.js

//tests/unit/components/*.js
test('component with optional block', function(assert) {
  assert.expect(1);

  var component = this.subject();
  Ember.run(function(){
    component.set('template', function(){ return 'Something else'; });
    component.set('defaultContent', 'foo');
  });
  
  assert.trimEq(this.$().text(), 'Something else');
});