Integration Testing in ASP.NET Core

Introduction

Integration tests hit ShopNest API through WebApplicationFactory — real HTTP pipeline, real middleware, test database — catching wiring bugs unit tests miss.

After this article you will

• Use WebApplicationFactory for in-memory test server
• Call endpoints with HttpClient and assert responses
• Configure SQLite or test SQL Server database
• Authenticate test requests with JWT or test auth handler
• Reset database state between tests with fixtures

Prerequisites

• Article 54 — Unit Testing with xUnit and Moq
• ShopNest Order Service / API from prior modules

Concept deep-dive

public class ShopNestApiFactory : WebApplicationFactory<Program>
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            var descriptor = services.SingleOrDefault(
                d => d.ServiceType == typeof(DbContextOptions<ShopNestDbContext>));
            if (descriptor != null) services.Remove(descriptor);

            services.AddDbContext<ShopNestDbContext>(options =>
                options.UseSqlite("DataSource=file:shopnest-test.db?mode=memory&cache=shared"));
        });
        builder.UseEnvironment("Testing");
    }
}

[Fact]
public async Task PostOrder_Returns201()
{
    var client = _factory.CreateClient();
    client.DefaultRequestHeaders.Authorization =
        new AuthenticationHeaderValue("Bearer", _factory.GetTestJwt());

    var response = await client.PostAsJsonAsync("/api/v1/orders", validOrder);
    response.StatusCode.Should().Be(HttpStatusCode.Created);
}

Unit vs integration: Unit = fast, isolated logic. Integration = slower, tests HTTP + DI + DB together.

Hands-on — ShopNest REST API End-to-End Testing

1. ShopNest.Api.IntegrationTests project.
2. WebApplicationFactory + SQLite in-memory shared connection.
3. Seed products; POST order; GET order by id — full flow.
4. IClassFixture<ShopNestApiFactory> for shared factory.
5. Respawn or recreate DB per test class.

Common errors & best practices

• Sharing mutable DB without reset — test order dependency failures.
• Testing against production connection string — never.
• Not replacing external APIs — use TestServer handler or WireMock.

Interview questions

Q: WebApplicationFactory?
A: Boots full app in memory for HttpClient tests without Kestrel network.

Q: When integration vs unit?
A: Unit for logic; integration for routes, auth, serialization, EF queries together.

Q: Test auth?
A: Test auth handler, pre-generated JWT, or WebApplicationFactory custom claims.

Summary

• WebApplicationFactory enables realistic API tests
• SQLite in-memory fast for CI pipelines
• Integration suite catches DI and middleware bugs
• Fixtures share expensive startup once per class

Previous: Unit Testing with xUnit and Moq
Next: Testing EF Core

FAQ