Add comprehensive unit tests for IRC command handling and message formatting

- Implemented IrcCommandHandlerTests to cover various IRC commands including PING, JOIN, PART, and authentication scenarios.
- Added IrcMessageFormatterTests to validate message formatting for different message types such as text, images, files, and audio.
- Created IrcMessageTests to ensure correct parsing of IRC messages and handling of various command formats.
- Introduced TestHelpers to facilitate testing with mock connections and streams, including a FakeChatService and FakeEncryptionService for simulating chat behavior.

src/EchoHub.Tests/Irc/IrcClientConnectionTests.cs

@@ -0,0 +1,213 @@
+using EchoHub.Server.Irc;
+using Xunit;
+
+namespace EchoHub.Tests.Irc;
+
+public class IrcClientConnectionTests
+{
+    // ── Connection identity ──────────────────────────────────────────────
+
+    [Fact]
+    public void ConnectionId_StartsWithIrcPrefix()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        Assert.StartsWith("irc-", conn.ConnectionId);
+    }
+
+    [Fact]
+    public void ConnectionId_IsUnique()
+    {
+        var (conn1, _) = TestIrcConnectionFactory.Create();
+        var (conn2, _) = TestIrcConnectionFactory.Create();
+        Assert.NotEqual(conn1.ConnectionId, conn2.ConnectionId);
+    }
+
+    // ── Hostmask ─────────────────────────────────────────────────────────
+
+    [Fact]
+    public void Hostmask_WithNicknameAndUsername_FormatsCorrectly()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.Nickname = "alice";
+        conn.Username = "alice_user";
+
+        Assert.Equal("alice!alice_user@echohub", conn.Hostmask);
+    }
+
+    [Fact]
+    public void Hostmask_WithoutUsername_FallsBackToNickname()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.Nickname = "alice";
+
+        Assert.Equal("alice!alice@echohub", conn.Hostmask);
+    }
+
+    // ── I/O ──────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task ReadLineAsync_ReturnsInputLines()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create("PING", "PONG");
+
+        var line1 = await conn.ReadLineAsync(CancellationToken.None);
+        var line2 = await conn.ReadLineAsync(CancellationToken.None);
+
+        Assert.Equal("PING", line1);
+        Assert.Equal("PONG", line2);
+    }
+
+    [Fact]
+    public async Task ReadLineAsync_EndOfStream_ReturnsNull()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create("PING");
+
+        await conn.ReadLineAsync(CancellationToken.None); // consume "PING"
+        var result = await conn.ReadLineAsync(CancellationToken.None);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public async Task SendAsync_WritesToOutput()
+    {
+        var (conn, stream) = TestIrcConnectionFactory.Create();
+
+        await conn.SendAsync(":server 001 alice :Welcome!");
+
+        var output = stream.GetOutputLines();
+        Assert.Single(output);
+        Assert.Equal(":server 001 alice :Welcome!", output[0]);
+    }
+
+    [Fact]
+    public async Task SendAsync_MultipleLines_AllCaptured()
+    {
+        var (conn, stream) = TestIrcConnectionFactory.Create();
+
+        await conn.SendAsync("line1");
+        await conn.SendAsync("line2");
+        await conn.SendAsync("line3");
+
+        var output = stream.GetOutputLines();
+        Assert.Equal(3, output.Count);
+    }
+
+    [Fact]
+    public async Task SendNumericAsync_FormatsCorrectly()
+    {
+        var (conn, stream) = TestIrcConnectionFactory.Create();
+        conn.Nickname = "alice";
+
+        await conn.SendNumericAsync("testserver", "001", ":Welcome!");
+
+        var output = stream.GetOutputLines();
+        Assert.Single(output);
+        Assert.Equal(":testserver 001 alice :Welcome!", output[0]);
+    }
+
+    [Fact]
+    public async Task SendNumericAsync_NoNickname_UsesStar()
+    {
+        var (conn, stream) = TestIrcConnectionFactory.Create();
+
+        await conn.SendNumericAsync("testserver", "451", ":Not registered");
+
+        var output = stream.GetOutputLines();
+        Assert.Contains("*", output[0]);
+    }
+
+    // ── Thread-safe channel operations ───────────────────────────────────
+
+    [Fact]
+    public void JoinChannel_AddsChannel()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.JoinChannel("general");
+
+        Assert.True(conn.IsInChannel("general"));
+    }
+
+    [Fact]
+    public void LeaveChannel_RemovesChannel()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.JoinChannel("general");
+        conn.LeaveChannel("general");
+
+        Assert.False(conn.IsInChannel("general"));
+    }
+
+    [Fact]
+    public void IsInChannel_CaseInsensitive()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.JoinChannel("General");
+
+        Assert.True(conn.IsInChannel("general"));
+        Assert.True(conn.IsInChannel("GENERAL"));
+    }
+
+    [Fact]
+    public void GetJoinedChannels_ReturnsSnapshot()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+        conn.JoinChannel("general");
+        conn.JoinChannel("random");
+
+        var channels = conn.GetJoinedChannels();
+        Assert.Equal(2, channels.Count);
+        Assert.Contains("general", channels);
+        Assert.Contains("random", channels);
+
+        // Modifying the returned list shouldn't affect the connection state
+        channels.Clear();
+        Assert.True(conn.IsInChannel("general"));
+    }
+
+    [Fact]
+    public async Task JoinedChannels_ConcurrentAccess_DoesNotThrow()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+
+        // Simulate concurrent reads and writes (broadcaster reads while handler writes)
+        var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
+        var writerTask = Task.Run(async () =>
+        {
+            for (int i = 0; i < 1000 && !cts.IsCancellationRequested; i++)
+            {
+                conn.JoinChannel($"channel-{i}");
+                await Task.Yield();
+                if (i % 3 == 0) conn.LeaveChannel($"channel-{i}");
+            }
+        }, cts.Token);
+
+        var readerTask = Task.Run(async () =>
+        {
+            for (int i = 0; i < 1000 && !cts.IsCancellationRequested; i++)
+            {
+                _ = conn.IsInChannel($"channel-{i}");
+                _ = conn.GetJoinedChannels();
+                await Task.Yield();
+            }
+        }, cts.Token);
+
+        // Should complete without exceptions
+        await Task.WhenAll(writerTask, readerTask);
+    }
+
+    // ── Default state ────────────────────────────────────────────────────
+
+    [Fact]
+    public void NewConnection_IsNotRegistered()
+    {
+        var (conn, _) = TestIrcConnectionFactory.Create();
+
+        Assert.False(conn.IsRegistered);
+        Assert.False(conn.IsAuthenticated);
+        Assert.Null(conn.Nickname);
+        Assert.Null(conn.Username);
+        Assert.Null(conn.UserId);
+        Assert.Null(conn.AwayMessage);
+    }
+}