Assert DateTime the Right Way MSTest NUnit C# Code

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Introduction

When we write tests – unit, integration, UI, etc. we often need to assert DateTime objects. However, the framework’s built-in methods not always can help us. If you compare your expected DateTime with the real one, they usually won’t be equal because of the seconds, milliseconds, etc. Because of that we need a better way to assert DateTimes with some delta.

For example if you want to compare:

2014.10.10 20:20:19 and 2014.10.10 20:20:20

These DateTimes are almost equal to a 1-second difference. In most cases, 1 seconds is not a problem. So you need an assert method that can be configured to ignore the 1-second discrepancy.

How to Assert DateTime in NUnit

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

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 your own 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 specific delta count.

public static class DateTimeAssert
{
    public static void Validate(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;
    }
}

The private method GetTimeSpanDeltaByType is used to calculate the total seconds based on the Delta Type.

In order for the main Assert method to work in all cases (expectedDate > actualDate or expectedDate < actualDate), we use Math.Abs when we calculate the total of the actual and expected DateTimes subtraction.

The usage is pretty simple:

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

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Source Code

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