dotnet-testing-advanced-webapi-integration-testing_skill

Overview

This skill is an advanced, practical guide for ASP.NET Core WebApi integration testing focused on end-to-end scenarios and standardized error verification. It documents how to build a repeatable test infrastructure using WebApplicationFactory, Testcontainers multi-container setups, Flurl for URL building, and AwesomeAssertions for precise HTTP response checks. The content emphasizes validating ProblemDetails and ValidationProblemDetails formats and modern IExceptionHandler-based error handling.

How this skill works

The skill shows how to create a TestWebApplicationFactory that orchestrates PostgreSQL and Redis containers, replaces services like a TimeProvider, and configures the app for a Testing environment. Tests use a Collection Fixture to share the factory, an IntegrationTestBase for common setup/teardown, Flurl to construct request URLs, and AwesomeAssertions to assert HTTP status codes and deserialized ProblemDetails payloads. It also explains implementing IExceptionHandler handlers (including FluentValidation) to produce RFC7807-compliant error responses.

When to use it

• When you need reliable end-to-end integration tests for ASP.NET Core WebApi endpoints
• When verifying API error formats (ProblemDetails / ValidationProblemDetails) and status codes
• When tests require dependent services like PostgreSQL and Redis in isolated containers
• When you want to assert HTTP responses and response bodies with expressive assertions
• When simulating time-sensitive behavior using a replaceable TimeProvider

Best practices

• Keep each test focused: follow Arrange, Act, Assert and one responsibility per test
• Register specialized exception handlers (e.g., FluentValidation) before generic handlers
• Share container resources via Collection Fixture to reduce startup overhead
• Clean or reset database state between tests (use Respawn or database cleanup scripts)
• Use Flurl for readable query construction and AwesomeAssertions for precise HTTP checks

Example use cases

• CreateProduct test that asserts 201 Created and validates returned product DTO
• Validation error test that asserts 400 BadRequest with ValidationProblemDetails errors
• GetById test that asserts 404 NotFound with ProblemDetails describing missing resource
• Paged query test using Flurl to build query string and asserting PagedResult structure
• Multi-container integration test where PostgreSQL and Redis are started for the suite