DateTime Interface to be used for unit testing

Question

Hi So I have created an interface for datetime like this:

public interface ITimeProvider<T>
{
    T Now { get; }
    string ToShortDateString();
}

And then I have one implamentation of that interface like this:

public class DateTimeProvider : ITimeProvider<DateTime>
{

    private DateTime _date;

    public DateTime Now
    {
        get { return DateTime.Now; }
    }

    public  DateTimeProvider()
    {

        _date = new DateTime();
    }
    public string ToShortDateString()
    {
        return _date.ToShortDateString();
    }
}

Then I am using it in my main unit and want to use property injection but i ran into some problems, here is a snap of what I have:

public class Atm : IAtm
{
   public ITimeProvider _timeProvider { get;set; }
}

This doesn't work as I don't specifiy a type. I could just do

public ITimeProvider<DateTime> _timeProvider { get;set; }

But then I wouldn't be able to use another timeprovider. I have also considered(and is the only solution I could come up with) is to make ATM generic so something like this

 public class Atm<T> : IAtm
 {
      public ITimeProvider<T> _timeProvider { get;set; }
 }

But then I feel like I can't use property injection, is there any other way I can do this so I will be able to test it?

"but I ran into some problems". "doesn't work as I don't specify a type", but you have registered your implementation of the interface with the injection container I assume? — Lasse V. Karlsen, Oct 29 '15 at 13:58
*“But then I wouldn't be able to use another timeprovider”* – How likely is it that you are considering using a different type than `DateTime` to represent dates and times? — poke, Oct 29 '15 at 14:04
You only need to be able to mock `DateTime.Now` for testing (which you are with that time provider). There is no reason to encapsulate the whole `DateTime` type; you can just create the datetime objects the way you need it for testing purposes. — poke, Oct 29 '15 at 14:09
@Sumsar1812 - Can you please explain why do you need `DateTime` to be a generic type parameter? — Channs, Oct 29 '15 at 14:19
To me there is just an easier way. Any class that relies on DateTime.Now checks.........just have an extra constructor property called "DateTime compareDate"..........then any non unit-test code will just pass in DateTime.Now...and a unittest can pass in a coded date. I never randomly code "DateTime.Now" in my classes...it is always passed in from "above". — granadaCoder, Oct 29 '15 at 14:29

Scott Chamberlain · Accepted Answer · 2019-12-20T19:38:27.423

The thing you are abstracting is the DateTime.Now function not the DateTime datatype, you can keep the implementation the exactly the same but just fix the type.

public interface ITimeProvider
{
    DateTime Now { get; }
    string ToShortDateString();
}

public class DateTimeProvider : ITimeProvider
{

    public DateTime Now
    {
        get { return DateTime.Now; }
    }

    public string ToShortDateString()
    {
        return Now.ToShortDateString();
    }
}


public class RemoteTimeProvider : ITimeProvider
{
    public DateTime Now
    {
        get 
        { 
            using(var client = new WebClient())
            {
                var timeString = client.DownloadString(http://www.timeapi.org/utc/now);
                return DateTime.Parse(timeString, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal).ToLocalTime()
            }

        }
    }

    public  DateTimeProvider()
    {

    }
    public string ToShortDateString()
    {
        //ToDo
    }
}

Also, I don't really get what your ToShortDateString() does, it does not take in a parameter and it just uses the value returned from new DateTime().

Ralf de Kleine · Answer 2 · 2015-10-29T14:15:54.853

Use Fakes to be able to unit test system or other assemblies not under your control.

[TestClass]
public class TestClass1
{ 
        [TestMethod]
        public void TestCurrentYear()
        {
            int fixedYear = 2000;

            // Shims can be used only in a ShimsContext:
            using (ShimsContext.Create())
            {
                // Arrange:
                // Shim DateTime.Now to return a fixed date:
                System.Fakes.ShimDateTime.NowGet = 
                () =>
                { return new DateTime(fixedYear, 1, 1); };

                // Instantiate the component under test:
                var componentUnderTest = new MyComponent();

                // Act:
                int year = componentUnderTest.GetTheCurrentYear();

                // Assert: 
                // This will always be true if the component is working:
                Assert.AreEqual(fixedYear, year);
            }
        }
}

DateTime Interface to be used for unit testing

2 Answers2

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