Assert DateTime the Right Way MSTest NUnit C# Code

How to Assert DateTime in NUnit

NUnit has added built-in support for this using the keyword Within.

DateTime now = DateTime.Now;
DateTime later = now + TimeSpan.FromHours(1.0);

Assert.That(later.Is.EqualTo(now).Within(TimeSpan.FromHours(3.0));
Assert.That(later, Is.EqualTo(now).Within(3).Hours;

So you don’t need to write a logic to test DateTimes.

How to Assert DateTime in MSTest

You will need an enum and a static class. The enum will hold the delta DateTime types- Seconds, Minutes, etc.

public enum DateTimeDeltaType
{
    Days,
    Minutes
}

Next use the below class to assert DateTimes with particular delta count.

public static class DateTimeAssert
{
    public static void AreEqual(DateTime? expectedDate, DateTime? actualDate, DateTimeDeltaType deltaType, int count)
    {
        if (expectedDate == null && actualDate == null)
        {
            return;
        }
        else if (expectedDate == null)
        {
            throw new NullReferenceException("The expected date was null");
        }
        else if (actualDate == null)
        {
            throw new NullReferenceException("The actual date was null");
        }
        TimeSpan expectedDelta = GetTimeSpanDeltaByType(deltaType, count);
        double totalSecondsDifference = Math.Abs(((DateTime)actualDate – (DateTime)expectedDate).TotalSeconds);

        if (totalSecondsDifference > expectedDelta.TotalSeconds)
        {
            throw new Exception(string.Format("Expected Date: {0}, Actual Date: {1} \nExpected Delta: {2}, Actual Delta in seconds- {3} (Delta Type: {4})",
                                            expectedDate,
                                            actualDate,
                                            expectedDelta,
                                            totalSecondsDifference,
                                            deltaType));
        }
    }

    private static TimeSpan GetTimeSpanDeltaByType(DateTimeDeltaType type, int count)
    {
        TimeSpan result = default(TimeSpan);

        switch (type)
        {
            case DateTimeDeltaType.Days:
                result = new TimeSpan(count, 0, 0, 0);
                break;
            case DateTimeDeltaType.Minutes:
                result = new TimeSpan(0, count, 0);
                break;
            default: throw new NotImplementedException("The delta type is not implemented.");
        }

        return result;
    }
}

DateTimeAssert.AreEqual(
    new DateTime(2014, 10, 10, 20, 22, 16),
    new DateTime(2014, 10, 11, 20, 22, 16),
    DateTimeDeltaType.Days,
    1);

Improved Version

Almost half year after initial publication, I created an even better implementation of the class. Credits go to my great readers in CodeProject. Thank you!

public static class DateTimeAssert
{
    public static void AreEqual(DateTime? expectedDate, DateTime? actualDate, TimeSpan maximumDelta)
    {
        if (expectedDate == null && actualDate == null)
        {
            return;
        }
        else if (expectedDate == null)
        {
            throw new NullReferenceException("The expected date was null");
        }
        else if (actualDate == null)
        {
            throw new NullReferenceException("The actual date was null");
        }
        double totalSecondsDifference = Math.Abs(((DateTime)actualDate – (DateTime)expectedDate).TotalSeconds);

        if (totalSecondsDifference > maximumDelta.TotalSeconds)
        {
            throw new Exception(string.Format("Expected Date: {0}, Actual Date: {1} \nExpected Delta: {2}, Actual Delta in seconds- {3}",
                                            expectedDate,
                                            actualDate,
                                            maximumDelta,
                                            totalSecondsDifference));
        }
    }
}

This version usage is more expressive and gives the freedom to use any Delta:

DateTimeAssert.AreEqual(
    new DateTime(2014, 10, 10, 20, 22, 16),
    new DateTime(2014, 10, 11, 20, 22, 16),
    TimeSpan.FromMilliSeconds(500);
DateTimeAssert.AreEqual(
    new DateTime(2014, 10, 10, 20, 22, 16),
    new DateTime(2014, 10, 11, 20, 22, 16),
    TimeSpan.FromMinutes(0.5); // half a minute = 30s