test(event-subscriber): project zaak-created notifications into the read projection (refs #7)

Failing unit + acceptance tests for the Event Subscriber's NotificationProjector:
a zaken/zaak/create notification yields one INGEDIEND projection row, duplicate
deliveries collapse to one row, non-zaak/non-create notifications are ignored, and
a rebuild repopulates the projection from the durable notification log (PRD §8.4).

The projector is a no-op stub so the tests compile and fail on the assertions; the
implementation follows in the green commit. The notification log doubles as the
idempotency guard and rebuild source so a rebuild needs no OpenZaak access (§8.1).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/event-subscriber/EventSubscriber.Tests/NotificationProjectorTests.cs

@@ -0,0 +1,69 @@
+using EventSubscriber.Application;
+
+namespace EventSubscriber.Tests;
+
+/// <summary>Behaviour of the projector that turns NRC notifications into projection rows.
+/// The walking skeleton reacts only to a zaak being created (status INGEDIEND) and must
+/// tolerate duplicate and out-of-order deliveries (CLAUDE.md §8.6).</summary>
+public sealed class NotificationProjectorTests
+{
+    private const string ZaakUrl = "http://openzaak:8000/zaken/api/v1/zaken/11111111-1111-1111-1111-111111111111";
+
+    private readonly InMemoryNotificationLog _log = new();
+    private readonly InMemoryProjectionStore _store = new();
+
+    private NotificationProjector Projector() => new(_log, _store);
+
+    private static Notification ZaakCreated(string url = ZaakUrl)
+        => new("zaken", "zaak", "create", new Uri(url));
+
+    [Fact]
+    public async Task creating_a_zaak_writes_one_row_with_status_ingediend()
+    {
+        await Projector().HandleAsync(ZaakCreated());
+
+        var entry = Assert.Single(await _store.AllAsync());
+        Assert.Equal("11111111-1111-1111-1111-111111111111", entry.Id);
+        Assert.Equal(RegistrationStatus.Ingediend, entry.Status);
+    }
+
+    [Fact]
+    public async Task replaying_the_same_notification_keeps_a_single_row()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        await projector.HandleAsync(ZaakCreated());
+
+        Assert.Single(await _store.AllAsync());
+    }
+
+    [Fact]
+    public async Task a_notification_on_another_kanaal_is_ignored()
+    {
+        await Projector().HandleAsync(new Notification("documenten", "enkelvoudiginformatieobject", "create", new Uri(ZaakUrl)));
+
+        Assert.Empty(await _store.AllAsync());
+    }
+
+    [Fact]
+    public async Task a_zaak_update_is_ignored_by_the_minimal_projection()
+    {
+        await Projector().HandleAsync(new Notification("zaken", "zaak", "update", new Uri(ZaakUrl)));
+
+        Assert.Empty(await _store.AllAsync());
+    }
+
+    [Fact]
+    public async Task rebuild_repopulates_the_projection_from_the_notification_log()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        await _store.ClearAsync();
+        Assert.Empty(await _store.AllAsync());
+
+        await projector.RebuildAsync();
+
+        var entry = Assert.Single(await _store.AllAsync());
+        Assert.Equal(RegistrationStatus.Ingediend, entry.Status);
+    }
+}