In a lot of our AD testing stuff we want to compare the results against some backend (ideally FiniteDifferences, in practice often ForwardDiff). I wonder if it might be a nice ergonomic improvement to be able to specify that directly somehow when constructing a scenario? i.e. make a one-liner for what's currently

ref_grad = DifferentiationInterface.gradient(f, reference_adtype, x)
scen = Scenario{:gradient,:out}(f, x; res1=ref_grad)

It's certainly easy for me to define a wrapper function but I'm lazy :-)

Although now I look at it, it seems like that might entail some awkward design choices for in-place operations like deepcopying x.