Integration Testing

1public class ProductsApiTests(WebApplicationFactory<Program> factory) : IClassFixture<WebApplicationFactory<Program>>
2{
3    [Fact]
4    public async Task Create_then_get()
5    {
6        var client = factory.CreateClient();
7        var response = await client.PostAsJsonAsync("/api/products", new { name = "Mouse", price = 799 });
8        Assert.Equal(HttpStatusCode.Created, response.StatusCode);
9    }
10}

1// Program.cs
2// (in the API project)
3using Microsoft.EntityFrameworkCore;
4

5var builder = WebApplication.CreateBuilder(args);
6builder.Services.AddControllers();
7builder.Services.AddDbContext<CatalogDb>(o => o.UseSqlServer(builder.Configuration.GetConnectionString("Catalog")));
8var app = builder.Build();
9app.MapControllers();
10app.Run();
11

12public partial class Program;                                        // lets the test project see Program
13

14// Data/CatalogDb.cs
15using System.ComponentModel.DataAnnotations;
16using Microsoft.EntityFrameworkCore;
17

18public class CatalogItem
19{
20    public int Id { get; set; }
21    [MaxLength(100)] public string Name { get; set; } = "";
22    public decimal Price { get; set; }
23}
24

25public class CatalogDb(DbContextOptions<CatalogDb> options) : DbContext(options)
26{
27    public DbSet<CatalogItem> Items => Set<CatalogItem>();
28}
29

30// Controllers/ProductsController.cs
31using System.ComponentModel.DataAnnotations;
32using Microsoft.AspNetCore.Mvc;
33

34public record CreateItemDto([Required, StringLength(100)] string Name, [Range(1, 1_000_000)] decimal Price);
35

36[ApiController]
37[Route("api/products")]
38public class ProductsController(CatalogDb db) : ControllerBase
39{
40    [HttpGet("{id:int}")]
41    public async Task<ActionResult<CatalogItem>> Get(int id) => await db.Items.FindAsync(id) is { } item ? item : NotFound();
42

43    [HttpPost]
44    public async Task<ActionResult<CatalogItem>> Create(CreateItemDto dto)
45    {
46        var item = new CatalogItem { Name = dto.Name, Price = dto.Price };
47        db.Items.Add(item);
48        await db.SaveChangesAsync();
49        return CreatedAtAction(nameof(Get), new { id = item.Id }, item);
50    }
51}
52

53// Tests/ApiFactory.cs
54// (in the test project, which references the API project)
55using Microsoft.AspNetCore.Hosting;
56using Microsoft.AspNetCore.Mvc.Testing;
57using Microsoft.AspNetCore.TestHost;
58using Microsoft.EntityFrameworkCore;
59using Microsoft.EntityFrameworkCore.Infrastructure;
60using Microsoft.Extensions.DependencyInjection;
61using Microsoft.Extensions.DependencyInjection.Extensions;
62

63public class ApiFactory : WebApplicationFactory<Program>
64{
65    private readonly string _databaseName = 
quot;tests-{Guid.NewGuid()}";
66

67    protected override void ConfigureWebHost(IWebHostBuilder builder) =>
68        builder.ConfigureTestServices(services =>
69        {
70            // Drop the SQL Server registration. EF Core 9 stores the UseSqlServer call in
71            // IDbContextOptionsConfiguration<T>, so remove that too or both providers end up registered.
72            services.RemoveAll<DbContextOptions<CatalogDb>>();
73            services.RemoveAll<IDbContextOptionsConfiguration<CatalogDb>>();
74            services.AddDbContext<CatalogDb>(o => o.UseInMemoryDatabase(_databaseName));
75        });
76}
77

78// Tests/ProductsApiTests.cs
79using System.Net;
80using System.Net.Http.Json;
81using System.Text.Json;
82using Xunit;
83

84public class ProductsApiTests(ApiFactory factory) : IClassFixture<ApiFactory>
85{
86    [Fact]
87    public async Task Post_then_get_returns_the_same_product()
88    {
89        var client = factory.CreateClient();
90

91        var created = await client.PostAsJsonAsync("/api/products", new { name = "Wireless Mouse", price = 799 });
92

93        Assert.Equal(HttpStatusCode.Created, created.StatusCode);
94        var item = await client.GetFromJsonAsync<JsonElement>(created.Headers.Location);
95        Assert.Equal("Wireless Mouse", item.GetProperty("name").GetString());
96    }
97

98    [Fact]
99    public async Task Post_with_invalid_body_returns_validation_problem()
100    {
101        var client = factory.CreateClient();
102

103        var response = await client.PostAsJsonAsync("/api/products", new { name = "", price = 0 });
104

105        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
106        Assert.Equal("application/problem+json", response.Content.Headers.ContentType?.MediaType);
107        var errors = (await response.Content.ReadFromJsonAsync<JsonElement>()).GetProperty("errors");
108        Assert.True(errors.TryGetProperty("Name", out _));
109        Assert.True(errors.TryGetProperty("Price", out _));
110    }
111

112    [Fact]
113    public async Task Get_unknown_id_returns_404()
114    {
115        var response = await factory.CreateClient().GetAsync("/api/products/12345");
116        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
117    }
118}

dotnet test runs the 3 tests against the real ASP.NET Core pipeline (routing, [ApiController] validation, JSON, EF Core with an in-memory database): Passed! - Failed: 0, Passed: 3, Skipped: 0, Total: 3.