Fiffi
Exploration kit for event driven services. Fiffi is a framework for code feedback of modeling. It forces some contracts on your infrastructure AND domain.
Core is the Fiffi IEvent envelope, EventRecord, ICommand, IQuery. Infrastructure is IAdvancedEventStore and ISnapshopStore.
Testing
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[Fact]
public async Task CreateGame()
{
//Given
context.Given(Array.Empty<IEvent>());
//When
await context.WhenAsync(new CreateGame { FirstTo = 3, GameId = Guid.NewGuid(), PlayerId = "tester", Title = "Test Game" });
//Then
context.Then((events, visual) => {
this.helper.WriteLine(visual);
Assert.True(events.OfType<GameCreated>().Happened());
});
}
At it's core is an definition of an IEventStore and the IEvent.
public interface IEventStore
{
Task<long> AppendToStreamAsync(string streamName, long version, IEvent[] events);
Task<(IEnumerable<IEvent> Events, long Version)> LoadEventStreamAsync(string streamName, int version);
}
The kit then focuses on creating a module of use cases with event driven state and flows.
The ApplicationService.ExecuteAsync is targeted on the infrastructure part of an application service.
ApplicationService.ExecuteAsync(
store,
command,
state => Array.Empty<IEvent>(),
events => pub(events)
)
The core Fiffi project also includes tools for handling command, query, event dispatching/routing, meta data and concurrency options.
The vision is to create a kit to get feedback/test from modeling/event storming sessions.
Modules
Using the Fiffi TestContext is based on using Modules. A boundary with a facade accepting commands, events and queries, it also publishes events - a key part of testing.
Testing With Modules
The first option would be using the configuration builder.
public class TestModule : Module
{
public TestModule(ModuleCore core) : base(core)
{ }
public static TestModule Initialize(IAdvancedEventStore store, ISnapshotStore snapshotStore, Func<IEvent[], Task> pub)
=> new Configuration<TestModule>(x => new TestModule(x))
.Commands(cmd => store.ExecuteAsync(cmd, "test", () => new[] { new TestEventRecord("test") }, pub))
.Updates(events => snapshotStore.Apply("test", new TestView(0), events.Select(x => x.Event), Apply))
.Triggers((events, dispatcher) => Task.CompletedTask)
.Query<TestQuery, TestView?>(q => snapshotStore.Get<TestView>("test"))
.Create(store);
public record TestView(int EventCount) : View;
public static TestView Apply(
TestView snap,
EventRecord @event) => snap with { EventCount = snap.EventCount + 1 };
public record TestQuery() : IQuery<TestView?>;
}
Creating a TestContext for integration tests using test extension
Using the TestModule we use the TestHost and TextContext, constructed by an extension.
(host, context) = Host.CreateDefaultBuilder()
.ConfigureWebHostDefaults(webBuilder =>
webBuilder.ConfigureServices(services =>
services
.AddFiffiInMemory()
.AddModule(TestModule.Initialize)
.AddInMemoryEventSubscribers()
)
.Configure(app => app.UseWelcomePage()))
.CreateFiffiTestContext(TestModule.Initialize);
In a "real" scenario the services configuration would be in Program or equivalent, so we could user the IHostBuilder. The replacement of Fiffi infrastructure would also be done via test services.
.CreateFiffiTestContext(
testServices => testServices.AddFiffiInMemory(),
TestModule.Initialize);
The Fiffi CreateFiffiTestContext replaces the subject module and event subscribers (with a test spy and additional test modules).
Armed with the host and context we could start authoring a simple test.
[Fact]
public async Task SimpleEventCaptureAsync()
{
await host.StartAsync();
await context.WhenAsync(new TestCommand(new AggregateId("test")));
context.Then((events, visual) => Assert.True(events.Happened<TestEventRecord>()));
await context.ThenAsync(new TestModule.TestQuery(), result => Assert.Equal(1, result.EventCount));
}
The TestContext offers a Given, When, Then (GWT) approach to interact with the subject module (and additional modules). A visualization extension also offers a ascii timeline, that you could output via your test framework.
The GWT approach also lets us build a current state by a history of events, by building event envelopes for testing.
[Fact]
public async Task HistoryEventCaptureAsync()
{
await host.StartAsync();
context.Given(EventEnvelope //todo extension
.Create("test", new TestEventRecord("test"))
.AddTestMetaData("test"));
await context.WhenAsync(new TestCommand(new AggregateId("test")));
context.Then((events, visual) => Assert.True(events.Happened<TestEventRecord>()));
await context.ThenAsync(new TestModule.TestQuery(), result => Assert.Equal(2, result.EventCount));
}
The TestContext will apply the history of events to the configured event store and projections, based on stream meta data and module configuration.
Creating a TestContext for integration tests using context builder
If you don't need/want easy access to the ServiceProvider you could initiate the Host within the Creation of the subject module, illustrated by the RPS sample.
this.context = TestContextBuilder.Create<InMemoryEventStore, GameModule>((store, pub) =>
{
this.helper = outputHelper;
var module = GameModule.Initialize(store, new InMemorySnapshotStore(), pub);
hostBuilder = RPS.Web.Program.CreateHostBuilder(Array.Empty<string>())
.ConfigureWebHost(webHost => webHost
.UseTestServer()
.ConfigureTestServices(services =>
services
.AddSingleton(module)
.Remove(services.SingleOrDefault(x => x.ImplementationType == typeof(ChangeFeedHostedService)))
));
return module;
});
Alternative way of authoring modules
An alternative to the more functional builder describe above, is to implement the IModule interface.
public class TestInterfaceModule : IModule
{
readonly IAdvancedEventStore store;
readonly ISnapshotStore snapshotStore;
readonly Func<IEvent[], Task> pub;
public TestInterfaceModule(IAdvancedEventStore store, ISnapshotStore snapshotStore, Func<IEvent[], Task> pub)
{
this.store = store;
this.snapshotStore = snapshotStore;
this.pub = pub;
}
public Task DispatchAsync(ICommand command) =>
store.ExecuteAsync(command, "test", () => new[] { new TestEventRecord("test") }, pub);
public Task OnStart(IEvent[] events) => WhenAsync(events);
public async Task<T?> QueryAsync<T>(IQuery<T> q) where T : class
=> await (q switch
{
TestQuery => snapshotStore.Get<T>("test"),
_ => throw new InvalidOperationException()
});
public IAsyncEnumerable<T> QueryAsync<T>(IStreamQuery<T> q)
=> throw new NotImplementedException();
public Task WhenAsync(params IEvent[] events) =>
snapshotStore.Apply("test", new TestView(0), events.Select(x => x.Event), Apply);
}
Note that there is no Update or Trigger methods in IModule. In the builder version a few thing are done under the hood, to aid startup and run updates before triggers. In the IModule version you handle OnStart and WhenAsync your self.
