Testing ASP.NET Core Applications

70 min

ASP.NET Core is designed with testability in mind, using dependency injection, interfaces, and separation of concerns to enable comprehensive testing. The framework's architecture makes it easy to test components in isolation. Testing ensures code quality, prevents regressions, and enables confident refactoring. Understanding testing enables professional application development. Testing is essential for maintainable applications.

You can unit test controllers, services, and middleware in isolation by mocking dependencies and testing behavior. Unit tests verify individual components work correctly. Mocking frameworks (Moq, NSubstitute) enable replacing dependencies with test doubles. Understanding unit testing enables component-level verification. Unit tests are fast and focused.

Integration tests allow you to test the entire application stack, including database, middleware, and routing. Integration tests verify components work together correctly. ASP.NET Core provides WebApplicationFactory for creating test servers. Understanding integration testing enables end-to-end verification. Integration tests are slower but more comprehensive.

Test frameworks include xUnit (recommended), NUnit, and MSTest. xUnit is the default for ASP.NET Core templates. Test frameworks provide attributes, assertions, and test runners. Understanding test frameworks enables writing effective tests. xUnit is modern and well-suited for ASP.NET Core.

Testing best practices include writing tests before or alongside code (TDD), testing edge cases and error conditions, keeping tests independent, using meaningful test names, and maintaining high test coverage. Understanding testing best practices enables effective test suites. Good tests are maintainable and reliable.

Best practices include using dependency injection for testability, mocking external dependencies, testing both success and failure paths, using test databases for integration tests, and maintaining test code quality. Understanding testing enables maintainable, reliable applications. Testing is essential for professional development.

Key Concepts

ASP.NET Core is designed with testability in mind.
Unit tests verify components in isolation.
Integration tests verify the entire application stack.
Dependency injection enables testability.
Test frameworks (xUnit, NUnit) provide testing infrastructure.

Learning Objectives

Master

Writing unit tests for controllers, services, and middleware
Writing integration tests for applications
Using mocking frameworks for dependencies
Following testing best practices

Develop

Test-driven development thinking
Understanding testing strategies
Writing maintainable test suites

Tips

Use dependency injection to enable testability.
Mock external dependencies in unit tests.
Test both success and failure paths.
Keep tests independent—don't rely on test execution order.

Common Pitfalls

Not writing tests, making refactoring risky.
Testing implementation details instead of behavior.
Creating tests that depend on each other.
Not maintaining tests, causing them to become outdated.

Summary

ASP.NET Core is designed for testability.
Unit tests verify components in isolation.
Integration tests verify the entire stack.
Understanding testing enables maintainable applications.
Testing is essential for professional development.

Exercise

Write unit tests for a controller and integration tests for the application.

// ProductControllerTests.cs
public class ProductControllerTests
{
    [Fact]
    public void Index_ReturnsViewResult()
    {
        // Arrange
        var mockService = new Mock<IProductService>();
        var controller = new ProductsController(mockService.Object);
        
        // Act
        var result = controller.Index();
        
        // Assert
        Assert.IsType<ViewResult>(result);
    }
}

// Integration test
public class ProductApiTests : IClassFixture<WebApplicationFactory<Program>>
{
    private readonly WebApplicationFactory<Program> _factory;
    
    public ProductApiTests(WebApplicationFactory<Program> factory)
    {
        _factory = factory;
    }
    
    [Fact]
    public async Task GetProducts_ReturnsSuccessStatusCode()
    {
        var client = _factory.CreateClient();
        var response = await client.GetAsync("/api/products");
        response.EnsureSuccessStatusCode();
    }
}

Testing ASP.NET Core Applications