test(integration): stop one failed SQL Server connect from failing every test

tests/NetEvolve.Pulse.Tests.Integration/Internals/Services/SqlServerContainerFixture.cs

@@ -15,10 +15,36 @@ public sealed class SqlServerContainerFixture : IAsyncDisposable, IAsyncInitiali
 
     private MsSqlContainer? _container;
 
+    // Pool Blocking Period=NeverBlock: by default SqlClient caches a failed open for 5 s to 1 min and rethrows it for
+    // every open on the same pool. All test databases are created through this one connection string, so a single
+    // failed connect would otherwise fail every fixture that initializes in that window.
     public string ConnectionString =>
         (
             _container ?? throw new InvalidOperationException("The SQL Server container has not been started.")
-        ).GetConnectionString() + ";MultipleActiveResultSets=True;";
+        ).GetConnectionString() + ";MultipleActiveResultSets=True;Pool Blocking Period=NeverBlock;";
+
+    // The tail of the container output, to tell a crashed SQL Server (microsoft/mssql-docker#974) from a network issue.
+    internal async Task<string> GetDiagnosticsAsync()
+    {
+        if (_container is null)
+        {
+            return "The SQL Server container has not been started.";
+        }
+
+        try
+        {
+            var (stdout, stderr) = await _container.GetLogsAsync().ConfigureAwait(false);
+            var tail = string.Join(
+                Environment.NewLine,
+                $"{stdout}{stderr}".Split('\n', StringSplitOptions.RemoveEmptyEntries).TakeLast(40)
+            );
+            return $"SQL Server container {_container.Id} output (last 40 lines):{Environment.NewLine}{tail}";
+        }
+        catch (Exception ex)
+        {
+            return $"Reading the SQL Server container output failed: {ex.Message}";
+        }
+    }
 
     public ValueTask DisposeAsync() => _container?.DisposeAsync() ?? ValueTask.CompletedTask;
 

tests/NetEvolve.Pulse.Tests.Integration/Internals/Services/SqlServerDatabaseServiceFixture.cs

@@ -21,54 +21,89 @@ public sealed class SqlServerDatabaseServiceFixture : IServiceFixture
     // ("Could not obtain exclusive lock on database 'model'"), so creation is serialized per test session.
     private const int ModelLockErrorNumber = 1807;
 
+    private const int MaxAttempts = 5;
+
     private static readonly SemaphoreSlim CreateDatabaseLock = new(1, 1);
 
+    // Set once connecting has failed MaxAttempts times. Creation is serialized, so without it every remaining fixture
+    // would wait through the same connect timeouts against an unreachable server.
+    private static Exception? _serverUnreachable;
+
     public async Task InitializeAsync()
     {
         await CreateDatabaseLock.WaitAsync().ConfigureAwait(false);
         try
         {
-            // Bounded retry in case 'model' is briefly held by SQL Server itself (e.g. right after startup).
-            for (var attempt = 1; attempt < 5; attempt++)
+            if (_serverUnreachable is not null)
             {
-                try
-                {
-                    await CreateDatabaseAsync().ConfigureAwait(false);
-                    return;
-                }
-                catch (SqlException ex) when (ex.Number == ModelLockErrorNumber)
-                {
-                    await Task.Delay(TimeSpan.FromMilliseconds(500 * attempt)).ConfigureAwait(false);
-                }
+                throw new InvalidOperationException(
+                    $"Failed to create SQL Server test database '{DatabaseName}': SQL Server was unreachable earlier in this test session.",
+                    _serverUnreachable
+                );
             }
 
-            await CreateDatabaseAsync().ConfigureAwait(false);
-        }
-        catch (Exception ex)
-        {
-            throw new InvalidOperationException($"Failed to create SQL Server test database '{DatabaseName}'.", ex);
+            try
+            {
+                await CreateDatabaseAsync(Container.ConnectionString, DatabaseName).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                var diagnostics = await Container.GetDiagnosticsAsync().ConfigureAwait(false);
+                throw new InvalidOperationException(
+                    $"Failed to create SQL Server test database '{DatabaseName}'.{Environment.NewLine}{diagnostics}",
+                    ex
+                );
+            }
         }
         finally
         {
             _ = CreateDatabaseLock.Release();
         }
     }
 
-    private async Task CreateDatabaseAsync()
+    private static async Task CreateDatabaseAsync(string connectionString, string databaseName)
     {
-        var con = new SqlConnection(Container.ConnectionString);
-        await using (con.ConfigureAwait(false))
+        // Bounded retry: the connect fails transiently (managed SNI error 35 on Linux, which SqlClient does not treat
+        // as transient, see dotnet/SqlClient#4665), or 'model' is briefly held by SQL Server itself (e.g. right after
+        // startup).
+        for (var attempt = 1; attempt <= MaxAttempts; attempt++)
         {
-            await con.OpenAsync().ConfigureAwait(false);
-
-            var cmd = con.CreateCommand();
-            await using (cmd.ConfigureAwait(false))
+            var con = new SqlConnection(connectionString);
+            await using (con.ConfigureAwait(false))
             {
+                try
+                {
+                    await con.OpenAsync().ConfigureAwait(false);
+                }
+                catch (SqlException ex)
+                {
+                    if (attempt == MaxAttempts)
+                    {
+                        _serverUnreachable = ex;
+                        throw;
+                    }
+
+                    await Task.Delay(TimeSpan.FromSeconds(attempt)).ConfigureAwait(false);
+                    continue;
+                }
+
+                try
+                {
+                    var cmd = con.CreateCommand();
+                    await using (cmd.ConfigureAwait(false))
+                    {
 #pragma warning disable CA2100, S2077 // Review SQL queries for security vulnerabilities; DatabaseName is test-controlled, not user input
-                cmd.CommandText = $"CREATE DATABASE [{DatabaseName}]";
+                        cmd.CommandText = $"CREATE DATABASE [{databaseName}]";
 #pragma warning restore CA2100, S2077
 
-                _ = await cmd.ExecuteNonQueryAsync().ConfigureAwait(false);
+                        _ = await cmd.ExecuteNonQueryAsync().ConfigureAwait(false);
+                        return;
+                    }
+                }
+                catch (SqlException ex) when (ex.Number == ModelLockErrorNumber && attempt < MaxAttempts)
+                {
+                    await Task.Delay(TimeSpan.FromMilliseconds(500 * attempt)).ConfigureAwait(false);
+                }
             }
         }
     }