MagicCSharp.Testing 1.0.2

MagicCSharp.Testing

Test doubles for the framework's own seams, so a test of a use case is new PlaceOrderUseCase(...) and an assertion. No test framework dependency, no database, no containers — add MagicCSharp.Testing.Database when you need those.

The fakes for your interfaces — FakeOrdersRepository, a recording IEventDispatcher — are yours to write, a few lines each against the interface the use case asked for. What ships here is the doubles for the seams the framework owns:

dotnet add package MagicCSharp.Testing

A use case, directly

var timeProvider = new FakeTimeProvider(new DateTimeOffset(2026, 3, 1, 0, 0, 0, TimeSpan.Zero));

var applyLateFees = new ApplyLateFeesUseCase(new FakeLeasesRepository(), timeProvider);

timeProvider.Advance(TimeSpan.FromDays(31));
await applyLateFees.Execute();

FakeTimeProvider comes from Microsoft's Microsoft.Extensions.TimeProvider.Testing, which this package references. SetUtcNow and Advance move it — forward only; it refuses to go back. Because it is .NET's own abstraction it also fakes what waits on time: Task.Delay(delay, timeProvider), PeriodicTimer and timed CancellationTokenSources complete when the test moves the clock, so a background service's loop can be tested without waiting for it.

Wiring a host

For a test that boots the application — WebApplicationFactory, or a ServiceCollection of your own — replace the framework's registrations:

var timeProvider = new FakeTimeProvider(new DateTimeOffset(2026, 3, 1, 0, 0, 0, TimeSpan.Zero));

services.RemoveAll<TimeProvider>();
services.AddSingleton<TimeProvider>(timeProvider);

services.RemoveAll<IKeyGenService>();
services.AddSingleton<IKeyGenService>(new FakeKeyGen(timeProvider));

services.RemoveAll<IDistributedLockProvider>();
services.AddSingleton<IDistributedLockProvider, InMemoryDistributedLockProvider>();

services.RemoveAll<IEventDispatcher>();
services.AddSingleton<IEventDispatcher>(sp =>
    new SyncEventDispatcher(sp.GetRequiredService<IAsyncEventDispatcher>()));

Asserting on events

await createOrder.Execute(new CreateOrderRequest { UserId = 1, ProductIds = [2, 3] });

Assert.True(eventDispatcher.HasDispatchedEvent<OrderCreatedEvent>());
Assert.Single(eventDispatcher.GetDispatchedEvents<OrderCreatedEvent>());
Assert.True(eventDispatcher.HasDispatchedEvent<OrderCreatedEvent>(orderCreatedEvent => orderCreatedEvent.UserId == 1));

DispatchedEvents is everything in order; ClearDispatchedEvents() resets between phases of one test.

One deliberate difference from production

SyncEventDispatcher runs handlers inline, inside whatever lock the emitting use case holds. In production dispatch is fire-and-forget, so handlers run after that lock is released. InMemoryDistributedLockProvider closes the gap: while SyncEventDispatcher is dispatching, a handler re-acquiring a name the emitter holds gets a no-op handle rather than deadlocking. The window is scoped to that one dispatch, so genuinely concurrent flows still get ordinary mutual exclusion.

Related packages

• MagicCSharp.Testing.Database — repository tests against a real PostgreSQL in a container
• MagicCSharp — the seams these replace

The whole picture, and the optional repository layout: github.com/MagicDoorInc/MagicCSharp. MIT.