Fix integration test infrastructure

- Create CustomWebApplicationFactory to properly handle DI
- Fix IntegrationTestBase to use proper service scope pattern
- Update AuthIntegrationTests and EventsIntegrationTests to use CustomWebApplicationFactory
- Resolve EF Core provider conflict by using ConfigureWebHost override

Tests now run: 7 passed, 6 failed (auth/response format issues)

tests/integration/backend/IntegrationTestBase.cs

@@ -1,3 +1,4 @@
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
@@ -9,41 +10,51 @@ using Xunit;
 
 namespace backend.Tests.Integration;
 
-public class IntegrationTestBase : IClassFixture<WebApplicationFactory<Program>>
+public class CustomWebApplicationFactory : WebApplicationFactory<Program>
 {
-    protected readonly WebApplicationFactory<Program> _factory;
-    protected readonly HttpClient _client;
-    protected readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
-
-    public IntegrationTestBase(WebApplicationFactory<Program> factory)
+    protected override void ConfigureWebHost(IWebHostBuilder builder)
     {
-        _factory = factory.WithWebHostBuilder(builder =>
+        builder.ConfigureServices(services =>
         {
-            builder.ConfigureServices(services =>
+            // Remove all DbContextOptions registrations
+            var descriptors = services.Where(
+                d => d.ServiceType == typeof(DbContextOptions<RacePlannerDbContext>) ||
+                     d.ServiceType.Name.Contains("DbContextOptions")).ToList();
+            
+            foreach (var descriptor in descriptors)
             {
-                // Replace the database context with an in-memory database
-                var descriptor = services.SingleOrDefault(
-                    d => d.ServiceType == typeof(DbContextOptions<RacePlannerDbContext>));
-                
-                if (descriptor != null)
-                {
-                    services.Remove(descriptor);
-                }
+                services.Remove(descriptor);
+            }
 
-                services.AddDbContext<RacePlannerDbContext>(options =>
-                {
-                    options.UseInMemoryDatabase("IntegrationTestDb");
-                });
-
-                // Ensure the database is created and seeded
-                var sp = services.BuildServiceProvider();
-                using var scope = sp.CreateScope();
-                var db = scope.ServiceProvider.GetRequiredService<RacePlannerDbContext>();
-                db.Database.EnsureCreated();
+            // Add in-memory database
+            services.AddDbContext<RacePlannerDbContext>(options =>
+            {
+                options.UseInMemoryDatabase(Guid.NewGuid().ToString());
             });
         });
+    }
+}
 
+public abstract class IntegrationTestBase : IClassFixture<CustomWebApplicationFactory>, IDisposable
+{
+    protected readonly CustomWebApplicationFactory _factory;
+    protected readonly HttpClient _client;
+    protected readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
+    protected readonly IServiceScope _scope;
+    protected readonly RacePlannerDbContext _dbContext;
+
+    protected IntegrationTestBase(CustomWebApplicationFactory factory)
+    {
+        _factory = factory;
         _client = _factory.CreateClient();
+        _scope = _factory.Services.CreateScope();
+        _dbContext = _scope.ServiceProvider.GetRequiredService<RacePlannerDbContext>();
+        _dbContext.Database.EnsureCreated();
+    }
+
+    public void Dispose()
+    {
+        _scope.Dispose();
     }
 
     protected HttpClient CreateAuthenticatedClient(string token = "")