Abstractions.DateAndTime

A simple library for abstracting the static properties in .NET's System.DateTime and System.DateTimeOffset.

The structs System.DateTime and System.DateTimeOffset each have a few static properties that are abstracted here in the following interfaces and their implementations:

• IDateTimeService - abstracts the Now, UtcNow and Today properties from System.DateTime.
• IDateTimeOffsetService - abstracts the Now and UtcNow properties from System.DateTimeOffset.

These abstractions can be faked, allowing for methods that access the system's date and time, to be unit tested.

Usage

In your application's services, wire up the dependencies that you require, using the extension methods in Abstractions.DateAndTime.Extensions.ServiceCollectionExtensions:

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddDateTimeService();
    services.AddDateTimeOffsetService();
    ...
}

The appropriate service can then be injected wherever it is required and then wherever DateTime.Now, DateTime.UtcNow, DateTime.Today, DateTimeOffset.Now or DateTimeOffset.UtcNow are used, replace them with a call to the corresponding abstraction:

private readonly IDateTimeService _dateTimeService;

public DateTimeHelper(IDateTimeService dateTimeService)
{
    _dateTimeService = dateTimeService ?? throw new ArgumentNullException(nameof(dateTimeService));
}

public string FormatCurrentDateTime()
{
    // return DateTime.Now.ToString();
    return _dateTimeService.Now().ToString();
}

Such code can then be unit tested by mocking the IDateTimeService or IDateTimeOffsetService instances:

private readonly IDateTimeHelper _dateTimeHelper;
private readonly IDateTimeService _dateTimeService;

public DateTimeHelperTests()
{
    _dateTimeService = A.Fake<IDateTimeService>();
    _dateTimeHelper = new DateTimeHelper(_dateTimeService);
}

[Test]
public void FormatCurrentDateTime_ReturnsCorrectlyFormattedDateTime()
{
    // Arrange
    A.CallTo(() => _dateTimeService.Now()).Returns(new DateTime(2021, 6, 20, 13, 21, 04));

    // Act
    var formattedCurrentDateTime = _dateTimeHelper.FormatCurrentDateTime();

    // Assert
    Assert.That(formattedCurrentDateTime, Is.EqualTo("20/06/2021 13:21:04"));
}

The above snippets are part of an example console application that consumes these abstractions and which can be found in this same repository here