stub with `yields`

api.route.js

describe("/api/foo/:id", function() {
  before(function() {
    var user = { foo: function() {} };
    var query = { complete: function() {} };
    var foo = "ok";
    // stub with yields
    sinon.stub(query, "complete").yields(null,  foo);
    sinon.stub(user, "foo").withArgs("1").returns(query);
    login(user);
  }); 
  after(function() {
    logout();
  }); 

  it("should respond with /api/foo/1.json", function(done) {
    request(app).get("/api/foo/1.json").set("Authorization", "Bearer " + token)
      .expect("Content-Type", "application/json")
      .expect(200)
      .end(function(error, result) {
        if (error) { return done(error); }
        done();
      }); 
  }); 
);