How to stub Fluture?

Background

I am trying to convert a code snippet from good old Promises into something using Flutures and Sanctuary:

https://codesandbox.io/embed/q3z3p17rpj?codemirror=1

Problem

Now, usually, using Promises, I can uses a library like sinonjs to stub the promises, i.e. to fake their results, force to resolve, to reject, ect.

This is fundamental, as it helps one test several branch directions and make sure everything works as is supposed to.

With Flutures however, it is different. One cannot simply stub a Fluture and I didn't find any sinon-esque libraries that could help either.

Questions

1. How do you stub Flutures ?
2. Is there any specific recommendation to doing TDD with Flutures/Sanctuary?

I'm not sure, but those Flutures (this name! ... nevermind, API looks cool) are plain objects, just like promises. They only have more elaborate API and different behavior.

Moreover, you can easily create "mock" flutures with Future.of, Future.reject instead of doing some real API calls.

Yes, sinon contains sugar helpers like resolves, rejects but they are just wrappers that can be implemented with callsFake.

So, you can easily create stub that creates fluture like this.

someApi.someFun = sinon.stub().callsFake((arg) => {
    assert.equals(arg, 'spam');
    return Future.of('bar');
});

Then you can test it like any other API. The only problem is "asynchronicity", but that can be solved like proposed below.

// with async/await
it('spams with async', async () => {
    const result = await someApi.someFun('spam).promise();
    assert.equals(result, 'bar');
});

// or leveraging mocha's ability to wait for returned thenables
it('spams', async () => {
    return someApi.someFun('spam)
        .fork(
             (result) => { assert.equals(result, 'bar');},
             (error) => { /* ???? */ }
        )
        .promise();
});