How to write an Arbitrary instance for a type that wraps a function?

I have this type which wraps a function

newtype Transaction d e r = Transaction (d -> Either e (d,r))

...and I want to do quickcheck tests for its Functor & Applicative instances but the compiler complains that it doesn't have an Arbitrary instance.

I tried to do so but I'm stuck at generating the random function.

Thanks!

== UPDATE ==

The quickcheck properties are defined like this

type IdProperty f a = f a -> Bool
functorIdProp :: (Functor f, Eq (f a)) => IdProperty f a
functorIdProp x = (fmap id x) == id x

type CompositionProperty f a b c = f a -> Fun a b -> Fun b c -> Bool
functorCompProp :: (Functor f, Eq (f c)) => CompositionProperty f a b c
functorCompProp x (apply -> f) (apply -> g) = (fmap (g . f) x) == (fmap g . fmap f $ x)

instance (Arbitrary ((->) d  (Either e (d, a)))) => Arbitrary (DbTr d e a) where
    arbitrary = do
      f <- ...???
      return $ Transaction f

...and the tests look like this:

spec = do
  describe "Functor properties for (Transaction Int String)" $ do
    it "IdProperty (Transaction Int String) Int" $ do
      property (functorIdProp :: IdProperty (Transaction Int String) Int)

    it "CompositionProperty (Transaction Int String) Int String Float" $ do
      property (functorCompProp :: CompositionProperty (Transaction Int String) Int String Float)