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
– Lasse V. Karlsen, Commented Oct 29, 2015 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
– poke, Commented Oct 29, 2015 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
– poke, Commented Oct 29, 2015 at 14:09
@Sumsar1812 - Can you please explain why do you need DateTime to be a generic type parameter? — Channs
– Channs, Commented Oct 29, 2015 at 14:19

Scott Chamberlain · Accepted Answer · 2019-12-20 19:38:27Z

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 · Accepted Answer · 2015-10-29 14:15:54Z

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); } } }

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