test(backend/Infrastructure): add integration tests for TaskRepository and ConversationService

Implemented comprehensive integration tests for TaskRepository and ConversationService using SQL Server and PostgreSQL Testcontainers. These tests cover various functionalities including adding, retrieving, updating, and deleting tasks and conversation threads, ensuring data integrity and expected behavior.

Modified files (3):
- TaskRepositoryTests.cs: Added tests for task CRUD operations and search functionality
- ConversationServiceTests.cs: Added tests for conversation thread management and message retrieval
- TaskAgent.Infrastructure.IntegrationTests.csproj: Configured project dependencies for integration testing

Author: cristofima

src/backend/services/TaskAgent/tests/TaskAgent.Infrastructure.IntegrationTests/Fixtures/PostgreSqlContainerFixture.cs

@@ -0,0 +1,63 @@
+using DotNet.Testcontainers.Builders;
+using Microsoft.EntityFrameworkCore;
+using TaskAgent.Infrastructure.Data;
+using Testcontainers.PostgreSql;
+
+namespace TaskAgent.Infrastructure.IntegrationTests.Fixtures;
+
+/// <summary>
+/// Shared PostgreSQL container fixture for xUnit Collection.
+/// This fixture starts a single PostgreSQL container that is shared across all tests in the collection.
+/// </summary>
+public class PostgreSqlContainerFixture : IAsyncLifetime
+{
+    private readonly PostgreSqlContainer _container;
+
+    public string ConnectionString { get; private set; } = string.Empty;
+
+    public PostgreSqlContainerFixture()
+    {
+        _container = new PostgreSqlBuilder()
+            .WithImage("postgres:16-alpine")
+            .WithDatabase("taskagent_integration_test")
+            .WithUsername("test_user")
+            .WithPassword("test_password")
+            .WithWaitStrategy(Wait.ForUnixContainer().UntilCommandIsCompleted("pg_isready", "-U", "test_user"))
+            .Build();
+    }
+
+    public async Task InitializeAsync()
+    {
+        await _container.StartAsync();
+        ConnectionString = _container.GetConnectionString();
+
+        // Create initial database schema
+        await using ConversationDbContext context = CreateDbContext();
+        await context.Database.EnsureCreatedAsync();
+    }
+
+    public async Task DisposeAsync() => await _container.DisposeAsync();
+
+    /// <summary>
+    /// Creates a new DbContext instance connected to the test container.
+    /// </summary>
+    public ConversationDbContext CreateDbContext()
+    {
+        DbContextOptions<ConversationDbContext> options = new DbContextOptionsBuilder<ConversationDbContext>()
+            .UseNpgsql(ConnectionString)
+            .Options;
+
+        return new ConversationDbContext(options);
+    }
+}
+
+/// <summary>
+/// xUnit Collection Definition for PostgreSQL tests.
+/// Tests marked with [Collection("PostgreSql")] will share the same container instance.
+/// </summary>
+[CollectionDefinition("PostgreSql")]
+#pragma warning disable CA1711 // Identifiers should not have incorrect suffix
+public class PostgreSqlCollection : ICollectionFixture<PostgreSqlContainerFixture>
+#pragma warning restore CA1711
+{
+}

src/backend/services/TaskAgent/tests/TaskAgent.Infrastructure.IntegrationTests/Fixtures/SqlServerContainerFixture.cs

@@ -0,0 +1,60 @@
+using DotNet.Testcontainers.Builders;
+using Microsoft.EntityFrameworkCore;
+using TaskAgent.Infrastructure.Data;
+using Testcontainers.MsSql;
+
+namespace TaskAgent.Infrastructure.IntegrationTests.Fixtures;
+
+/// <summary>
+/// Shared SQL Server container fixture for xUnit Collection.
+/// This fixture starts a single SQL Server container that is shared across all tests in the collection.
+/// </summary>
+public class SqlServerContainerFixture : IAsyncLifetime
+{
+    private readonly MsSqlContainer _container;
+
+    public string ConnectionString { get; private set; } = string.Empty;
+
+    public SqlServerContainerFixture()
+    {
+        _container = new MsSqlBuilder()
+            .WithImage("mcr.microsoft.com/mssql/server:2022-latest")
+            .WithWaitStrategy(Wait.ForUnixContainer().UntilPortIsAvailable(1433))
+            .Build();
+    }
+
+    public async Task InitializeAsync()
+    {
+        await _container.StartAsync();
+        ConnectionString = _container.GetConnectionString();
+
+        // Create initial database schema
+        await using TaskDbContext context = CreateDbContext();
+        await context.Database.EnsureCreatedAsync();
+    }
+
+    public async Task DisposeAsync() => await _container.DisposeAsync();
+
+    /// <summary>
+    /// Creates a new DbContext instance connected to the test container.
+    /// </summary>
+    public TaskDbContext CreateDbContext()
+    {
+        DbContextOptions<TaskDbContext> options = new DbContextOptionsBuilder<TaskDbContext>()
+            .UseSqlServer(ConnectionString)
+            .Options;
+
+        return new TaskDbContext(options);
+    }
+}
+
+/// <summary>
+/// xUnit Collection Definition for SQL Server tests.
+/// Tests marked with [Collection("SqlServer")] will share the same container instance.
+/// </summary>
+[CollectionDefinition("SqlServer")]
+#pragma warning disable CA1711 // Identifiers should not have incorrect suffix
+public class SqlServerCollection : ICollectionFixture<SqlServerContainerFixture>
+#pragma warning restore CA1711
+{
+}