test: HowToSubscribeRealModel replayed earlier runs — LiteDbFactory left LiteDB's journal behind; in-memory assertion db + own-row bounded counts

src/MicroPlumberd.Tests.App/Infrastructure/InMemoryAssertionDb.cs

@@ -37,13 +37,11 @@ public void Add(Metadata m, object evt)
 
 public class LiteDbFactory
 {
-    private static int _id = 0;
-
-    public static LiteDatabase Get()
-    {
-        string fileName = $"./test_{Interlocked.Increment(ref _id)}.db";
-        if(File.Exists(fileName))
-            File.Delete(fileName);
-        return new LiteDatabase(fileName);
-    }
+    /// <summary>
+    /// A fresh, empty, IN-MEMORY LiteDB per call. It was a file, ./test_{n}.db, "fresh" by deleting that file — but LiteDB
+    /// also writes a journal, ./test_{n}-log.db, which survived and was REPLAYED on the next open: a later process's
+    /// HowToSubscribeRealModel counted earlier runs' reservations ("found 2", "found 6", 10 — growing run on run, and
+    /// passing only where the journal had been checkpointed away). Memory leaves nothing behind for the next run.
+    /// </summary>
+    public static LiteDatabase Get() => new LiteDatabase(new MemoryStream());
 }

src/MicroPlumberd.Tests/HowTo/PlumberMethodsTests.cs

@@ -82,12 +82,16 @@ public async Task HowToSubscribeRealModel()
             await plumber.SubscribeEventHandler(dbModel);
 
             var suffixOfStreamWhereOurEventWillBeAppend = Guid.NewGuid();
-            var ourLovelyEvent = new TicketReserved() { MovieName = "Golden Eye", RoomName = "101"};
+            // THIS row's own reservation, by its own name. The "found 2/6" reds were a LiteDB journal replayed from earlier runs
+            // (fixed in LiteDbFactory); the class-fixture store contributes nothing TODAY (the absolute-count mutant survives) —
+            // but the model subscribes from the beginning, so the next row in this class that reserves under a shared name would
+            // bring an absolute count's order-dependence back. Count ours.
+            var movie = $"Golden Eye {Guid.NewGuid():N}";
+            var ourLovelyEvent = new TicketReserved() { MovieName = movie, RoomName = "101"};
 
             await plumber.AppendEvent(ourLovelyEvent, suffixOfStreamWhereOurEventWillBeAppend);
-            await Task.Delay(1000);
 
-            dbModel.Reservations.Query().Count().Should().Be(1);
+            (await OwnReservationsFolded(dbModel.Reservations, movie)).Should().Be(1, "our event is folded exactly once");
 
         }
         [Fact]
@@ -102,12 +106,12 @@ public async Task HowToSubscribeRealModelWithHost()
                 .StartAsync();
 
             var suffixOfStreamWhereOurEventWillBeAppend = Guid.NewGuid();
-            var ourLovelyEvent = new TicketReserved() { MovieName = "Golden Eye", RoomName = "101" };
+            var movie = $"Golden Eye {Guid.NewGuid():N}"; // this row's own reservation (see HowToSubscribeRealModel)
+            var ourLovelyEvent = new TicketReserved() { MovieName = movie, RoomName = "101" };
 
             await sp.GetRequiredService<IPlumber>().AppendEvent(ourLovelyEvent, suffixOfStreamWhereOurEventWillBeAppend);
-            await Task.Delay(1000);
 
-            sp.GetRequiredService<LiteDatabase>().Reservations().Query().Count().Should().Be(1);
+            (await OwnReservationsFolded(sp.GetRequiredService<LiteDatabase>().Reservations(), movie)).Should().Be(1, "our event is folded exactly once");
 
         }
 
@@ -265,6 +269,19 @@ await plumber.Rehydrate(model, $"ReservationStream-{Guid.NewGuid()}",
         }
 
 
+        /// <summary>
+        /// Waits — bounded, for the condition the assertion needs: THIS row's reservation folded — instead of a fixed delay, then
+        /// gives a short settle so a duplicate delivery of the same event would still be counted. Returns how many are folded.
+        /// </summary>
+        private static async Task<int> OwnReservationsFolded(LiteDB.ILiteCollection<Reservation> reservations, string movie)
+        {
+            var deadline = DateTime.UtcNow + TimeSpan.FromSeconds(15);
+            while (reservations.Count(x => x.MovieName == movie) == 0 && DateTime.UtcNow < deadline)
+                await Task.Delay(50);
+            await Task.Delay(250);
+            return reservations.Count(x => x.MovieName == movie);
+        }
+
         public void Dispose()
         {
             _host?.Dispose();

src/MicroPlumberd.Tests/Unit/LiteDbFactoryTests.cs

@@ -0,0 +1,48 @@
+using FluentAssertions;
+using LiteDB;
+using MicroPlumberd.Tests.App.CinemaDomain;
+using MicroPlumberd.Tests.App.Infrastructure;
+
+namespace MicroPlumberd.Tests.Unit;
+
+/// <summary>
+/// HowToSubscribeRealModel counted reservations of EARLIER test runs: LiteDbFactory "freshened" ./test_{n}.db by deleting
+/// it, but LiteDB's journal ./test_{n}-log.db survived and was replayed on the next open ("found 2", "found 6", 10 — growing
+/// run on run). Two rows, because a file factory shows differently on the two kinds of bin (rev-reach):
+/// - CLEAN bin (CI, always): the file factory CREATES test_1.db — the no-file row is red; StartsEmpty is green (nothing to replay).
+/// - DIRTY bin (a dev's second run): it re-opens existing names — no new path, but the files are MODIFIED (the no-file row,
+///   by length + write time, is red). StartsEmpty is red only where a NOT-yet-checkpointed journal was left behind (as the
+///   HowTo rows left one: "found 11"); in this class's own runs it stayed green. The no-file row is the guard on both bins.
+/// A path-set-only form of the no-file row was blind on the dirty bin (names are reused); this one sees creation AND change.
+/// </summary>
+public class LiteDbFactoryTests
+{
+    [Fact]
+    public void AnAssertionDb_CreatesOrTouchesNoFile_ForALaterRunToReplay()
+    {
+        var dir = Directory.GetCurrentDirectory();
+        var before = Snapshot(dir);
+
+        using (var db = LiteDbFactory.Get())
+            db.Reservations().Insert(new Reservation { MovieName = "written", RoomName = "1" });
+
+        var after = Snapshot(dir);
+        var created = after.Keys.Except(before.Keys).ToList();
+        var modified = after.Where(f => before.TryGetValue(f.Key, out var was) && was != f.Value).Select(f => f.Key).ToList();
+        created.Concat(modified).Should().BeEmpty(
+            "an assertion db must leave nothing on disk — a file, or its journal, is replayed into the next run's model");
+    }
+
+    private static Dictionary<string, (long Length, DateTime Written)> Snapshot(string dir) =>
+        Directory.GetFiles(dir, "*.db").ToDictionary(f => f, f => { var i = new FileInfo(f); return (i.Length, i.LastWriteTimeUtc); });
+
+    [Fact]
+    public void EachAssertionDb_StartsEmpty()
+    {
+        using (var first = LiteDbFactory.Get())
+            first.Reservations().Insert(new Reservation { MovieName = "written", RoomName = "1" });
+
+        using var next = LiteDbFactory.Get();
+        next.Reservations().Count().Should().Be(0);
+    }
+}