Integration Testing

Overview

Integration testing validates interactions between components such as API layers, databases, queues, and external services.

Scope

• Service to database integration
• Service to service contract behavior
• Message publication and consumption
• Authentication and authorization flows

sequenceDiagram
    participant Test
    participant API
    participant DB
    Test->>API: POST /orders
    API->>DB: insert order
    DB-->>API: success
    API-->>Test: 201 Created

Practical Example

public class OrdersApiTests : IClassFixture<ApiTestFactory>
{
    private readonly HttpClient _client;

    public OrdersApiTests(ApiTestFactory factory)
    {
        _client = factory.CreateClient();
    }

    [Fact]
    public async Task CreateOrder_ReturnsCreated()
    {
        var payload = new { customerId = "cust-1", total = 149.90m };
        var response = await _client.PostAsJsonAsync("/orders", payload);

        Assert.Equal(HttpStatusCode.Created, response.StatusCode);
    }
}

Integration tests run against real dependencies in controlled environments.

Production Guidance

• Keep test data isolated per run
• Validate API contracts and persistence side effects
• Run in CI with deterministic environment setup

Common Pitfalls

• Sharing state between tests
• Depending on external unstable services
• Running integration suites too infrequently

Key Takeaways

• Integration tests catch boundary issues missed by unit tests.
• Deterministic environments reduce flaky behavior.
• Contract-focused assertions improve cross-service reliability.