unit test: favorite way to mock backbone endpoint and test callbacks, using `$ajax` and promise

unit_test_backbone_endpoint.js

//////////////////////////
// backbone fetch method
//////////////////////////

// set up fetch & callbacks
myCollection.fetch( options )
.done( this.successHandler.call( this ) )
.fail( this.errorHandler.call( this ) );

//////////////////////////
// unit test
//////////////////////////

// now we need to test that successHandler get called when the fetch is successful, 
// and errorHandler get called when it is not
it( "fetch is successful, successHandler get called", function() {
	var d =  new $.Deferred(),
		stub = sandbox.stub( $, "ajax" ).returns( d.promise() );

	// resolve the promise:
	d.resolve( { data: "bar" } );

	sandbox.stub( myCollection, "successHandler" );

	myCollection.fetch();

	expect( myCollection.successHandler ).to.have.been.calledWith( { data: "bar" } );
});

it( "fetch failed, errorHandler get called", function() {
	var d =  new $.Deferred(),
		stub = sandbox.stub( $, "ajax" ).returns( d.promise() );

	// reject the promise:
	d.reject( "foo1", "foo2", "foo3" );

	sandbox.stub( myCollection, "errorHandler" );

	myCollection.fetch();

	expect( myCollection.errorHandler ).to.have.been.calledWith( "foo1", "foo2", "foo3" );
});