sinon-mocking.js

it ( 'should calculate the proper value', function () {

  var ds = new DataService();
  var x = new Foo( ds );

  sinon.stub( ds, "lookupMultiplier" ).returns( 2 );

  var rst = x.calculateValueBasedOnLookup( 5 );

  expect( rst ).to.equal( 10 );

} );

it ( 'should send an email', function () {

  var es = new EmailService();
  var bar = new Bar( es );

  var expectation = sinon.mock( es )
    .expects( "send" ).withArgs( "hello" );

  bar.somethingThatSendsAnEmail();

  expectation.verify();

} );