Suggestion

test.js

var response_spy = sinon.spy();

$(document).on('recipes.response_details", response_spy);
$(document).trigger("recipes.request_details", { guid: "123"});

// Now there should be a  pending AJAX request to the server.

var req = this.last_xhr_request();

// You can inspect it ot make sure it's going to the right URL, etc. (look at other tests).

req.respond( ...... ); // Not sure of the syntax, but look in other tests to fill in the ajax response.

// Now that the AJAX has completed, we hsould have the response_spy data

equal(response_spy.calledCount, 1);

// And verify some of the fields...