Assert the result. Example: public class ProductsControllerTests { [Fact] public void Get_ReturnsOkResult_WithProducts() { // Arrange var mockService = new Mock<IProductService>(); mockService.Setup(s => s.GetAll()).Returns(new List<Product> { new Product { Id = 1, Name = "Laptop" } }); var controller = new ProductsController(mockService.Object); Follow : // Act var result = controller.Get(); // Assert var okResult = Assert.IsType<OkObjectResult>(result); var products = Assert.IsType<List<Product>>(okResult.Value); Assert.Single(products); } } ✅ Key: Mock all dependencies so controller is tested in isolation. 2⃣ How to Mock DbContext for Testing?

EF Core allows using InMemoryDatabase or mocking DbSet<T> to avoid hitting a real

database.

Example with InMemoryDatabase:

var options = new DbContextOptionsBuilder<AppDbContext>()

.UseInMemoryDatabase(databaseName: "TestDb")

.Options;

using var context = new AppDbContext(options);

context.Products.Add(new Product { Id = 1, Name = "Laptop" });

context.SaveChanges();

// Act

var service = new ProductService(context);

var products = service.GetAll();

// Assert

Assert.Single(products);

Example with Moq (for advanced mocking):

Follow :

var mockSet = new Mock<DbSet<Product>>();

var mockContext = new Mock<AppDbContext>();

mockContext.Setup(c => c.Products).Returns(mockSet.Object);

3⃣ What is Integration Testing in ASP.NET Core?

Integration tests test the application as a whole, including middleware, routing,

controllers, and database.

• Ensures all parts work together.
• Usually uses WebApplicationFactory for hosting the app in-memory.

Example:

public class ProductsApiTests :

IClassFixture<WebApplicationFactory<Program>>

private readonly HttpClient _client;

public ProductsApiTests(WebApplicationFactory<Program> factory)

_client = factory.CreateClient();

[Fact]

public async Task GetProducts_ReturnsOk()

var response = await _client.GetAsync("/api/products");

response.EnsureSuccessStatusCode();

var products = await

response.Content.ReadFromJsonAsync<List<Product>>();

Assert.NotNull(products);

Follow :

✅ Integration tests are slower but catch real runtime issues.

4⃣ How Do You Test Middleware?

Middleware can be tested by invoking it in isolation using RequestDelegate.

Example:

[Fact]

public async Task CustomMiddleware_SetsHeader()

// Arrange

var middleware = new CustomHeaderMiddleware(async

(innerHttpContext) =>

await innerHttpContext.Response.WriteAsync("Hello");

});

var context = new DefaultHttpContext();

// Act

await middleware.InvokeAsync(context);

// Assert

Assert.Equal("MyValue",

context.Response.Headers["X-Custom-Header"]);

✅ Test middleware without starting a real server.

5⃣ How to Use WebApplicationFactory for Testing?

Follow :

WebApplicationFactory<T> spins up your ASP.NET Core app in-memory, perfect for

integration tests or testing minimal APIs.

Example:

var factory = new WebApplicationFactory<Program>();

var client = factory.CreateClient();

var response = await client.GetAsync("/api/products");

response.EnsureSuccessStatusCode();

You can override services for testing:

var factory = new WebApplicationFactory<Program>()

.WithWebHostBuilder(builder =>

builder.ConfigureServices(services =>

services.AddDbContext<AppDbContext>(options =>

options.UseInMemoryDatabase("TestDb"));

});

});

6⃣ How to Test Minimal APIs?

Minimal APIs are tested using WebApplicationFactory or TestServer.

Example:

var factory = new WebApplicationFactory<Program>();

var client = factory.CreateClient();

var response = await client.GetAsync("/products");

var products = await

response.Content.ReadFromJsonAsync<List<Product>>();

Follow :

Assert.NotEmpty(products);

7⃣ What Frameworks Are Commonly Used?

• xUnit – Popular, lightweight, supports parallel testing.
• NUnit – Rich assertion library.
• MSTest – Microsoft-supported, integrated in Visual Studio.

Most modern ASP.NET Core projects use xUnit + Moq.

8⃣ How to Use Moq for Mocking Dependencies?

Moq creates fake implementations of interfaces to control behavior during tests.

Example:

var mockRepo = new Mock<IProductRepository>();

mockRepo.Setup(x => x.GetAll()).Returns(new List<Product> { new

Product { Id = 1, Name = "Laptop" } });

var service = new ProductService(mockRepo.Object);

var products = service.GetAll();

Assert.Single(products);

✅ Use .Setup(), .Verify(), and .Returns() to simulate behavior.

9⃣ How to Use InMemoryDatabase for EF Core Testing?

Follow :

EF Core InMemoryDatabase allows quick tests without SQL Server.

Steps: