sandbox.stub(Cars, "findOne",
            () => {return car1 });

Cars.find().fetch()

sandbox.stub(Cars, "find", () => {
    return {
        fetch: sinon.stub().returns(anything);
    };
});

//set up stub and spy
    const valSpy = sandbox.spy();
    const jQueryStub = sandbox
      .stub($.prototype, "find")       // this prototype is important
      .withArgs("input[name=email]")
      .returns({ val: valSpy });

    // call function under test
    learnerAlreadyAccepted(inviteDoc);

    // check expectations
    expect(jQueryStub).to.have.been.called;      // not really necessary
    expect(valSpy).to.have.been.calledWith("");

learnerAlreadyAccepted = function(doc) {
    $("form").find("input[name=email]").val("");
  }