func testButtonStateThreeTimes() {
    //1
    let scheduler = TestScheduler(initialClock: 0)

    //2
    let username = scheduler.createHotObservable([
            next(0, "A"),
            next(100, "B")
        ])

    //3
    let password = scheduler.createHotObservable([
            next(0, "ABC"),
            next(300, "ABCD")
        ])

    //4
    viewModel = LoginViewModel(input:
        (username: username.asObservable(),
          password: password.asObservable()
        )
    )

    //5
    var resultArray = [Bool]()
    viewModel.signInButtonEnabled
        .subscribeNext {
            resultArray.append($0)
        }
    .addDisposableTo(disposeBag)

    //6
    scheduler.start()

    //7
    XCTAssertEqual(resultArray, [false, false, true])
}