fix: complete retail parity stability pass

tests/AcDream.Core.Net.Tests/Transport/RetailPacketLossAveragerTests.cs

@@ -0,0 +1,77 @@
+using AcDream.Core.Net.Transport;
+
+namespace AcDream.Core.Net.Tests.Transport;
+
+public sealed class RetailPacketLossAveragerTests
+{
+    [Fact]
+    public void Sweep_BeforeRetailHeartbeat_DoesNotPublishPartialSample()
+    {
+        long now = 0;
+        var clock = new TransportClock(() => now, frequency: 10);
+        var stats = new TransportStats { PacketsSent = 5, NakIdsSent = 1 };
+        var sut = new RetailPacketLossAverager(clock, stats);
+
+        stats.PacketsSent += 10;
+        stats.NakIdsSent += 2;
+        now = 19;
+        sut.Sweep(now, stats);
+
+        Assert.Equal(0d, sut.Percentage);
+    }
+
+    [Fact]
+    public void Sweep_UsesRetailNakPlusRetransmitOverReceivedPlusSentFormula()
+    {
+        long now = 0;
+        var clock = new TransportClock(() => now, frequency: 10);
+        var stats = new TransportStats();
+        var sut = new RetailPacketLossAverager(clock, stats);
+
+        stats.PacketsSent = 60;
+        stats.PacketsReceived = 40;
+        stats.NakIdsSent = 2;
+        stats.ResendsSent = 3;
+        now = 20;
+        sut.Sweep(now, stats);
+
+        Assert.Equal(5d, sut.Percentage);
+    }
+
+    [Fact]
+    public void Sweep_EvictsTheOldestSampleAfterFortyHeartbeats()
+    {
+        long now = 0;
+        var clock = new TransportClock(() => now, frequency: 10);
+        var stats = new TransportStats();
+        var sut = new RetailPacketLossAverager(clock, stats);
+
+        stats.PacketsSent = 10;
+        stats.NakIdsSent = 10;
+        now = 20;
+        sut.Sweep(now, stats);
+
+        for (int i = 0; i < RetailPacketLossAverager.WindowSize; i++)
+        {
+            stats.PacketsSent += 10;
+            now += 20;
+            sut.Sweep(now, stats);
+        }
+
+        Assert.Equal(0d, sut.Percentage);
+    }
+
+    [Fact]
+    public void Sweep_ZeroTrafficReportsZero()
+    {
+        long now = 0;
+        var clock = new TransportClock(() => now, frequency: 10);
+        var stats = new TransportStats();
+        var sut = new RetailPacketLossAverager(clock, stats);
+
+        now = 20;
+        sut.Sweep(now, stats);
+
+        Assert.Equal(0d, sut.Percentage);
+    }
+}