testland/dotnet-faketime

Wraps .NET's TimeProvider abstraction (System.TimeProvider, introduced .NET 8) and FakeTimeProvider from Microsoft.Extensions.TimeProvider.Testing: SetUtcNow, Advance, AutoAdvanceAmount, CreateTimer, Delay, and the pre-.NET-8 ISystemClock migration path. Use when testing C# or F# code that reads the current time, uses timers, or awaits Task.Delay.

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Pre-.NET-8 pattern: ISystemClock migration

Name: testland/dotnet-faketime
Rating: 75.2 (1 reviews)
Author: testland

Before TimeProvider, the Microsoft.Extensions stack used ISystemClock (namespace Microsoft.Extensions.Internal, assembly Microsoft.Extensions.Caching.Abstractions.dll). Per learn.microsoft.com/dotnet/api/microsoft.extensions.internal.isystemclock: "Abstracts the system clock to facilitate testing." It exposed a single property, UtcNow, and carried the notice "This API supports the .NET infrastructure and is not intended to be used directly from your code."

// Legacy pattern (pre-.NET 8)
public interface ISystemClock
{
    DateTimeOffset UtcNow { get; }
}

// Test implementation
public class FakeSystemClock : ISystemClock
{
    public DateTimeOffset UtcNow { get; set; }
}

Migration path: replace ISystemClock injection with TimeProvider, and replace fake implementations with FakeTimeProvider. The ISystemClock approach covers only UtcNow; TimeProvider also covers high-frequency timestamps and timers, making it the complete replacement.