test(domain): cover clamd timeout, caller cancellation, null content and defaults (refs #192)

Domain mutation score 89.87% → 91.98%, back above the 90% break.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

services/domain/Big.Tests/ClamdDocumentScannerTests.cs

@@ -17,13 +17,14 @@ public class ClamdDocumentScannerTests
         public Task<byte[]> Received { get; }
         public int Port => ((IPEndPoint)_listener.LocalEndpoint).Port;
 
-        public FakeClamd(string reply)
+        /// <param name="reply">The answer, or null to accept the request and never answer (a hung clamd).</param>
+        public FakeClamd(string? reply)
         {
             _listener.Start();
             Received = Serve(reply);
         }
 
-        private async Task<byte[]> Serve(string reply)
+        private async Task<byte[]> Serve(string? reply)
         {
             using var client = await _listener.AcceptTcpClientAsync();
             var stream = client.GetStream();
@@ -35,7 +36,10 @@ public class ClamdDocumentScannerTests
                 if (n == 0) break;
                 received.Write(buffer, 0, n);
             }
-            await stream.WriteAsync(System.Text.Encoding.ASCII.GetBytes(reply + "\0"));
+            if (reply is null)
+                await Task.Delay(TimeSpan.FromSeconds(10)); // long past any test timeout
+            else
+                await stream.WriteAsync(System.Text.Encoding.ASCII.GetBytes(reply + "\0"));
             return received.ToArray();
         }
 
@@ -82,4 +86,32 @@ public class ClamdDocumentScannerTests
 
         Assert.Equal(ScanVerdict.Unavailable, await ScannerFor(port).ScanAsync([1, 2, 3]));
     }
+
+    [Fact]
+    public async Task A_clamd_that_never_answers_is_unavailable_after_the_timeout()
+    {
+        using var clamd = new FakeClamd(reply: null);
+        var scanner = new ClamdDocumentScanner(
+            new ClamAvOptions { Host = "127.0.0.1", Port = clamd.Port, Timeout = TimeSpan.FromMilliseconds(300) });
+
+        Assert.Equal(ScanVerdict.Unavailable, await scanner.ScanAsync([1, 2, 3]));
+    }
+
+    [Fact]
+    public async Task A_cancelled_request_is_cancelled_not_reported_unavailable()
+    {
+        // The caller giving up is not a scanner outage: it propagates instead of becoming a 503.
+        using var clamd = new FakeClamd(reply: null);
+        using var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(300));
+
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => ScannerFor(clamd.Port).ScanAsync([1, 2, 3], cts.Token));
+    }
+
+    [Fact]
+    public async Task Rejects_null_content()
+        => await Assert.ThrowsAsync<ArgumentNullException>(() => ScannerFor(1).ScanAsync(null!));
+
+    [Fact]
+    public void Defaults_to_the_clamav_service_on_the_clamd_port()
+        => Assert.Equal(("clamav", 3310), (new ClamAvOptions().Host, new ClamAvOptions().Port));
 }