public async Task ExecuteAsync_does_not_execute_if_cancel_requested()
        {
            const SaleState startState = SaleState.Open;
            var             sale       = new Sale(saleId: 66)
            {
                State = startState
            };
            var sut = new StateTransitionParameterized <Sale, SaleState, SaleEvent, string>(
                stateAccessor: saleToUpdate => saleToUpdate.State
                , stateMutator: (saleToUpdate, newState) => saleToUpdate.State = newState
                , toState: SaleState.Complete
                , conditionAsync: (_, stringParam, cancelToken) => Task.FromResult(result: true)
                , name: "test"
                , priority: 1);

            using var cancelSource = new CancellationTokenSource();
            {
                var cancelToken = cancelSource.Token;
                cancelSource.Cancel();
                var parameters = new ExecutionParameters <Sale, SaleEvent>(SaleEvent.Pay, sale, request: "notUsed", cancellationToken: cancelToken);

                var result = await sut.ExecuteAsync(parameters);

                Assert.True(result.WasCancelled);
                Assert.False(result.WasTransitioned);
                Assert.Equal(startState, sale.State);
            }
        }
        public void ExecuteAsync_ConditionAsync_can_be_cancelled()
        {
            const SaleState startState = SaleState.Open;
            var             sale       = new Sale(saleId: 66)
            {
                State = startState
            };
            var sut = new StateTransitionParameterized <Sale, SaleState, SaleEvent, string>(
                stateAccessor: saleToUpdate => saleToUpdate.State
                , stateMutator: (saleToUpdate, newState) => saleToUpdate.State = newState
                , toState: SaleState.Complete
                , conditionAsync: (_, stringParam, cancellationToken) =>
            {
                Task.Delay(millisecondsDelay: 999999, cancellationToken: cancellationToken);
                return(Task.FromResult(!cancellationToken.IsCancellationRequested));
            }
                , name: "test"
                , priority: 1);

            using var cancelSource = new CancellationTokenSource();
            var parameters = new ExecutionParameters <Sale, SaleEvent>(SaleEvent.Pay, sale, cancellationToken: cancelSource.Token);

            Task.Run(async() => await sut.ExecuteAsync(parameters, currentResult: null));
            cancelSource.Cancel();

            Assert.Equal(startState, sale.State);
        }
        public async Task ExecuteAsync_does_not_change_state_if_condition_not_met()
        {
            const SaleState startState = SaleState.Open;
            const SaleState endState   = SaleState.Complete;
            var             sale       = new Sale(saleId: 66)
            {
                State = startState
            };

            var sut = new StateTransitionParameterized <Sale, SaleState, SaleEvent, string>(
                stateAccessor: saleToUpdate => saleToUpdate.State
                , stateMutator: (saleToUpdate, newState) => saleToUpdate.State = newState
                , toState: endState
                , conditionAsync: (_, stringParam, inCancelToken) => Task.FromResult(result: false)
                , name: "test"
                , priority: 1);

            await sut.ExecuteAsync(new ExecutionParameters <Sale, SaleEvent>(SaleEvent.Pay, sale, request : "notUsed"));

            Assert.Equal(startState, sale.State);
        }
        public async Task ExecuteAsync_throws_ArgumentException_if_Request_is_wrong_type()
        {
            const SaleState startState = SaleState.Open;
            var             sale       = new Sale(saleId: 66)
            {
                State = startState
            };
            var sut = new StateTransitionParameterized <Sale, SaleState, SaleEvent, string>(
                stateAccessor: saleToUpdate => saleToUpdate.State
                , stateMutator: (saleToUpdate, newState) => saleToUpdate.State = newState
                , toState: SaleState.Complete
                , conditionAsync: (_, stringParam, cancelToken) => Task.FromResult(result: true)
                , name: "test"
                , priority: 1);

            using var cancelSource = new CancellationTokenSource();
            {
                var cancelToken     = cancelSource.Token;
                var executionParams = new ExecutionParameters <Sale, SaleEvent>(SaleEvent.Pay, sale, request: 1, cancellationToken: cancelToken);

                await Assert.ThrowsAsync <ArgumentException>(async() => await sut.ExecuteAsync(executionParams));
            }
        }