FakeTimeFixture

Assembly: FEFF.TestFixtures.AspNetCore.dll
Namespace: FEFF.TestFixtures.AspNetCore
Source: FakeTimeFixture.cs

Overview

The FakeTimeFixture is an extension to AppManagerFixture.
It replaces the TimeProvider service with a Microsoft.Extensions.Time.Testing.FakeTimeProvider singleton in the application under test, providing deterministic control over time-dependent behavior in your tests.

Key Features

Deterministic Time: Start time at a fixed point (2000-01-01 00:00:00 UTC) for reproducible tests
Dynamic Time Control: Adjust the current time during test execution using SetUtcNow()
Automatic Registration: Automatically registers the fake time provider with the application's DI container
Integration with AppManagerFixture: Works seamlessly with other ASP.NET Core fixtures

Basic Usage

First, define your test application entry point:

// ASP.NET Core test application entry point (Program.cs)
public class Program
{
    public static void Main(string[] args)
    {
        var builder = WebApplication.CreateBuilder(args);
        builder.Services.AddSingleton((_) => TimeProvider.System);
        var app = builder.Build();

        // Example endpoint that uses TimeProvider
        app.MapGet("/current-time", (TimeProvider timeProvider) =>
        {
            return timeProvider.GetUtcNow().ToString("yyyy-MM-dd");
        });

        app.Run();
    }
}

Note: TimeProvider should be registered as a singleton:

builder.Services.AddSingleton((_) => TimeProvider.System);

Then use the fixture in your tests:

using FEFF.TestFixtures.AspNetCore;
using Microsoft.Extensions.Time.Testing;

public class TimeTests
{
    protected IAppClientFixture Client { get; } = 
        TestContext.Current.GetFeffFixture<AppClientFixture<Program>>();

    protected FakeTimeFixture<Program> FakeTimeFx { get; } = 
        TestContext.Current.GetFeffFixture<FakeTimeFixture<Program>>();

    protected FakeTimeProvider FakeTime => FakeTimeFx.Value;

    [Fact]
    public async Task CurrentTime__should_respond_with_default_date()
    {
        // Default time is 2000-01-01 00:00:00 UTC
        var resp = await Client.LazyValue.GetAsync("/current-time", TestContext.Current.CancellationToken);
        var body = await resp.Content.ReadAsStringAsync(TestContext.Current.CancellationToken);

        body.Should().Be("\"2000-01-01\"");
    }

    [Theory]
    [InlineData("2006-01-05")]
    [InlineData("2150-11-15")]
    public async Task CurrentTime__should_respond_with_custom_date(string date)
    {
        // Set the fake time to a specific date
        FakeTime.SetUtcNow(DateTimeOffset.Parse($"{date}T05:05:05Z"));

        var resp = await Client.LazyValue.GetAsync("/current-time", TestContext.Current.CancellationToken);
        var body = await resp.Content.ReadAsStringAsync(TestContext.Current.CancellationToken);

        body.Should().Be($@"""{date}""");
    }
}

Type Arguments

Type Argument	Constraint	Description
`TEntryPoint`	`class`	The application entry point type. Typically the `Startup` or `Program` class.

Key Members

Member	Type	Description
`Value`	`FakeTimeProvider`	Gets the `FakeTimeProvider` instance. Can be used to control time during tests using methods like `SetUtcNow()` and `AdvanceDays()`.

Time Control Methods

The Microsoft.Extensions.Time.Testing.FakeTimeProvider provides several methods to control time:

Method	Description
`SetUtcNow(DateTimeOffset)`	Sets the current UTC time to a specific value
`AdvanceDays(int)`	Advances the current time by the specified number of days
`Advance(TimeSpan)`	Advances the current time by the specified time span

Tip

The FakeTimeProvider instance can be manipulated at any point during a test: before and after the application under test is started.

Link	Description
API: FakeTimeFixture	API reference
FakeTimeFixtureTests.cs	Unit tests for `FakeTimeFixture`
API Integration Example	Integration test examples using `FakeTimeFixture`
Microsoft.Extensions.Time.Testing Documentation	Official documentation for `FakeTimeProvider`

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