add InsinTelemetryDiscoveredPrintersReceiver decorator

Inspectron.Epson.Tests/Telemetry/InsinTelemetryDiscoveredPrintersReceiverTests.cs

@@ -0,0 +1,104 @@
+using EpsonPrintService;
+using Inspectron.Epson;
+using Inspectron.Epson.PrintServer.Telemetry;
+
+namespace Inspectron.Epson.Tests.Telemetry;
+
+public class InsinTelemetryDiscoveredPrintersReceiverTests
+{
+    private sealed class RecordingTelemetry : IInsinTelemetry
+    {
+        public List<(string Kind, string Message)> Events { get; } = new();
+        public void Emit(string kind, string message) => Events.Add((kind, message));
+    }
+
+    private sealed class CountingInner : IDiscoveredPrintersReceiver
+    {
+        public int Calls;
+        public Task OnPrintersDiscoveredAsync(IReadOnlyList<DiscoveredPrinter> printers)
+        {
+            Calls++;
+            return Task.CompletedTask;
+        }
+    }
+
+    private static DiscoveredPrinter Printer(string ip, string model = "TM-T30III") =>
+        new() { IPAddress = ip, ModelName = model };
+
+    [Fact]
+    public async Task First_sighting_emits_discovered_and_online()
+    {
+        var telemetry = new RecordingTelemetry();
+        var inner = new CountingInner();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(inner, telemetry);
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Equal(1, inner.Calls);
+        Assert.Collection(telemetry.Events,
+            e => Assert.Equal("printer.discovered", e.Kind),
+            e => Assert.Equal("printer.online",     e.Kind));
+        Assert.Contains("printer=192.168.1.10", telemetry.Events[0].Message);
+        Assert.Contains("model=TM-T30III",      telemetry.Events[0].Message);
+    }
+
+    [Fact]
+    public async Task Repeat_sighting_emits_nothing()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Empty(telemetry.Events);
+    }
+
+    [Fact]
+    public async Task Disappearance_emits_offline()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(Array.Empty<DiscoveredPrinter>());
+
+        Assert.Single(telemetry.Events);
+        Assert.Equal("printer.offline", telemetry.Events[0].Kind);
+        Assert.Equal("printer=192.168.1.10", telemetry.Events[0].Message);
+    }
+
+    [Fact]
+    public async Task Reappearance_emits_online_only_not_discovered()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        await sut.OnPrintersDiscoveredAsync(Array.Empty<DiscoveredPrinter>());
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Single(telemetry.Events);
+        Assert.Equal("printer.online", telemetry.Events[0].Kind);
+    }
+
+    [Fact]
+    public async Task Telemetry_failures_do_not_break_inner()
+    {
+        var telemetry = new ThrowingTelemetry();
+        var inner = new CountingInner();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(inner, telemetry);
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Equal(1, inner.Calls);
+    }
+
+    private sealed class ThrowingTelemetry : IInsinTelemetry
+    {
+        public void Emit(string kind, string message) => throw new InvalidOperationException("boom");
+    }
+}