Deferred

func testFuture() {

    let expectation1 = XCTestExpectation(description: self.debugDescription)
    var cancellables = Set<AnyCancellable>()

    let future = Future<Int, Error> { promise in
        promise(.success(42))
    }

    // Future自体は他のPubと全く同じように、Subされて初めて値を放出し始めるのだから、
    // Deferred なんていらないのでは？

    DispatchQueue.global().asyncAfter(deadline: .now() + 3) {
        future
            .assertNoFailure()
            .sink(
                receiveCompletion: { fini in
                    print(fini)
                },
                receiveValue: { print($0) }
            )
            .store(in: &cancellables)
    }

    wait(for: [expectation1], timeout: 10.0)
}