Unit testing for property which has sytem.DateTime value C#

Question

How to write unit testing for following code block where the

public class Hotel
{
    DateTime CLOSING_TIME // imported from somewhere else
    public bool IsOpen
    {
        get
        {
            return DateTime.Now <= CLOSING_TIME
        }
    }
}

I tried following either one will fail all the time, how can i make sure that both unit test case will pass every time:

[TestFixture]
public void ShouldBeOpen()
{
    var Hot= new Hotel();
    Assert.True(Hot.IsOpen); 
}

[TestFixture]
public void ShouldBeOpen()
{
    var Hot= new Hotel();
    Assert.False(Hot.IsOpen); 
}

Can someone please help?

Possible duplicate of [What's a good way to overwrite DateTime.Now during testing?](https://stackoverflow.com/questions/43711/whats-a-good-way-to-overwrite-datetime-now-during-testing) — FCin, Jul 26 '18 at 12:44
you should consider to only use the `TimeOfDay` of the `DateTime` or do you update your ClosingTime daily? — Marco Forberg, Jul 26 '18 at 12:56

Spotted · Answer 1 · 2018-07-26T13:25:50.193

There are many problems with your tests:

They are non-deterministic (as you already noticed) because they rely on time
They are redundant (the second test tests exactly the same as the first one)
From the semantic you typed it looks like you need to work with time and not a full DateTime, which you fail to express in IsOpen

I also personally think that such a trivial test is useless because it adds no value over this test:

[TestFixture]
public void ShouldBeOpen()
{
    Assert.True(DateTime.Now <= CLOSING_TIME);
}

However a slight change in IsOpen can improve both your implementation and testing code and keep your code simple (no need to stub/mock the system date):

public sealed class Hotel
{
    public bool IsOpenAt(DateTime time) => time.TimeOfDay <= CLOSING_TIME.TimeOfDay;
}

With such kind of tests which are really testing some business assertions:

[TestFixture]
public void ShouldBeOpen()
{
    Assert.True(new Hotel().IsOpenAt(CLOSING_TIME));
}

[TestFixture]
public void ShouldNotBeOpen()
{
    Assert.False(new Hotel().IsOpenAt(CLOSING_TIME.AddMinutes(1)));
}

Note

There is something I'd like to address although not requested: CLOSING_TIME. This field looks suspicious to me. Indeed, I suspect the way you set this value introduces unnecessary coupling from something with Hotel. If not the case, I would advocate that you request this value as a constructor's parameter to achieve a better decoupling:

public sealed class Hotel
{
    private readonly DateTime _closingTime;
    public Hotel(DateTime closingTime) => _closingTime = closingTime;
    public bool IsOpenAt(DateTime time) => time.TimeOfDay <= _closingTime.TimeOfDay;
}

Dan Scott · Answer 2 · 2018-07-26T13:18:27.747

The code below I threw together to mock a time interface that you can use for your unit tests. using this you can set your time to either the real time or a fake time that you specify. I often use this method when unit testing. It's called Dependency injection or constructor injection which is very useful for unit testing.

    class Hotel
    {
        public DateTime ClosingTime = DateTime.ParseExact("17:00:00", "HH:ii:ss", CultureInfo.InvariantCulture);
        public IStubClock Clock;
        public bool IsOpen
        {
            get
            {
                return Clock.Now.TimeOfDay <= ClosingTime.TimeOfDay;
            }
        }
        public Hotel(IStubClock clock)
        {
            Clock = clock;
        }
    }

Using this interface you can mock any DateTime.Now structure

    public interface IStubClock
    {
        DateTime Now { get; }
    }

A fake variant

    public class FakeClock : IStubClock
    {
        private DateTime _now;
        public DateTime Now
        {
            get
            {
                return _now;
            }
        }

        public FakeClock(DateTime now)
        {
            _now = now;
        }
    }

And a real variant

    public class RealClock : IStubClock
    {
        public DateTime Now
        {
            get
            {
                return DateTime.Now;
            }
        }
    }

and then you can use them in your tests doing something like this

    class Program
    {
        static void Main(string[] args)
        {
            IStubClock fakeClock = new FakeClock(new DateTime(1, 1, 1, 10, 0, 0)); //time is set to 10am
            IStubClock realClock = new RealClock(); //time is set to whatever the time now is.
            Hotel hotel1 = new Hotel(fakeClock); //using fake time
            Hotel hotel2 = new Hotel(realClock); //using the real time
        }
    }

Unit testing for property which has sytem.DateTime value C#

2 Answers2

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