Unit Testing

1var result = await controller.Get(7);
2var dto = Assert.IsType<ProductDto>(result.Value);          // returned the object
3Assert.IsType<NotFoundResult>(result.Result);                // returned NotFound()

1// Services/Pricing.cs
2public interface IProductRepository
3{
4    Task<ProductRecord?> FindAsync(int id);
5}
6

7public record ProductRecord(int Id, string Name, decimal Price, bool IsDiscontinued);
8public record ProductDto(int Id, string Name, decimal Price);
9

10public class PricingService
11{
12    public decimal PriceFor(decimal listPrice, int quantity, string? customerTier) =>
13        Math.Round(listPrice * quantity * (1 - (customerTier, quantity) switch
14        {
15            ("gold", _) => 0.15m,
16            (_, >= 10) => 0.05m,
17            _ => 0m,
18        }), 2);
19}
20

21// Controllers/ProductsController.cs
22using Microsoft.AspNetCore.Mvc;
23

24[ApiController]
25[Route("api/products")]
26public class ProductsController(IProductRepository products) : ControllerBase
27{
28    [HttpGet("{id:int}")]
29    public async Task<ActionResult<ProductDto>> Get(int id)
30    {
31        var product = await products.FindAsync(id);
32        if (product is null) return NotFound();
33        if (product.IsDiscontinued) return StatusCode(StatusCodes.Status410Gone);
34        return new ProductDto(product.Id, product.Name, product.Price);
35    }
36}
37

38// Tests/PricingServiceTests.cs
39using Xunit;
40

41public class PricingServiceTests
42{
43    private readonly PricingService _pricing = new();
44

45    [Theory]
46    [InlineData(100, 1, null, 100)]       // no discount
47    [InlineData(100, 10, null, 950)]      // 5% bulk discount from 10 items
48    [InlineData(100, 2, "gold", 170)]     // gold customers: 15% on any order
49    [InlineData(100, 10, "gold", 850)]    // gold beats bulk
50    public void PriceFor_applies_the_best_rule(int listPrice, int quantity, string? tier, int expected) =>
51        Assert.Equal(expected, _pricing.PriceFor(listPrice, quantity, tier));
52}
53

54// Tests/ProductsControllerTests.cs
55using Microsoft.AspNetCore.Mvc;
56using Moq;
57using Xunit;
58

59public class ProductsControllerTests
60{
61    private readonly Mock<IProductRepository> _repository = new();
62

63    [Fact]
64    public async Task Get_returns_the_dto_for_an_active_product()
65    {
66        _repository.Setup(r => r.FindAsync(7)).ReturnsAsync(new ProductRecord(7, "Wireless Mouse", 799m, false));
67

68        var result = await new ProductsController(_repository.Object).Get(7);
69

70        var dto = Assert.IsType<ProductDto>(result.Value);
71        Assert.Equal("Wireless Mouse", dto.Name);
72        _repository.Verify(r => r.FindAsync(7), Times.Once);
73    }
74

75    [Fact]
76    public async Task Get_returns_404_for_unknown_products()
77    {
78        var result = await new ProductsController(_repository.Object).Get(99);
79        Assert.IsType<NotFoundResult>(result.Result);
80    }
81

82    [Fact]
83    public async Task Get_returns_410_for_discontinued_products()
84    {
85        _repository.Setup(r => r.FindAsync(3)).ReturnsAsync(new ProductRecord(3, "Old Webcam", 999m, true));
86        var result = await new ProductsController(_repository.Object).Get(3);
87        Assert.Equal(410, Assert.IsType<StatusCodeResult>(result.Result).StatusCode);
88    }
89}

dotnet test runs 7 tests (4 Theory cases + 3 Facts): Passed! - Failed: 0, Passed: 7, Skipped: 0, Total: 7.