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Testing an ASP.NET Core web app with Testcontainers

Learn how to test an ASP.NET Core web app using Testcontainers for .NET with a real Microsoft SQL Server instance instead of SQLite.

Table of contents

In this guide, you'll learn how to:

  • Use Testcontainers for .NET to spin up a Microsoft SQL Server container for integration tests
  • Replace SQLite with a production-like database provider in ASP.NET Core tests
  • Customize WebApplicationFactory to configure test dependencies with Testcontainers
  • Manage container lifecycle with xUnit's IAsyncLifetime

Prerequisites

Note

If you're new to Testcontainers, visit the Testcontainers overview to learn more about Testcontainers and the benefits of using it.

Set up the project

Background

This guide builds on top of Microsoft's Integration tests in ASP.NET Core documentation. The original sample uses an in-memory SQLite database as the backing store for integration tests. You'll replace SQLite with a real Microsoft SQL Server instance running in a Docker container using Testcontainers.

You can find the original code sample in the dotnet/AspNetCore.Docs.Samples repository.

Clone the repository

Clone the Testcontainers guide repository and change into the project directory:

$ git clone https://github.com/testcontainers/tc-guide-testing-aspnet-core.git
$ cd tc-guide-testing-aspnet-core

Project structure

The solution contains two projects:

RazorPagesProject.sln
├── src/RazorPagesProject/              # ASP.NET Core Razor Pages app
└── tests/RazorPagesProject.Tests/      # xUnit integration tests

Application project

The application project (src/RazorPagesProject/RazorPagesProject.csproj) is a Razor Pages web app that uses Entity Framework Core with SQLite as its default database provider:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Identity.UI" Version="7.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="7.0.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  </ItemGroup>

</Project>

The ApplicationDbContext stores Message entities and provides methods to query and manage them:

public class ApplicationDbContext : IdentityDbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public virtual DbSet<Message> Messages { get; set; }

    public async virtual Task<List<Message>> GetMessagesAsync()
    {
        return await Messages
            .OrderBy(message => message.Text)
            .AsNoTracking()
            .ToListAsync();
    }

    public async virtual Task AddMessageAsync(Message message)
    {
        await Messages.AddAsync(message);
        await SaveChangesAsync();
    }

    public async virtual Task DeleteAllMessagesAsync()
    {
        foreach (Message message in Messages)
        {
            Messages.Remove(message);
        }

        await SaveChangesAsync();
    }

    public async virtual Task DeleteMessageAsync(int id)
    {
        var message = await Messages.FindAsync(id);

        if (message != null)
        {
            Messages.Remove(message);
            await SaveChangesAsync();
        }
    }

    public void Initialize()
    {
        Messages.AddRange(GetSeedingMessages());
        SaveChanges();
    }

    public static List<Message> GetSeedingMessages()
    {
        return new List<Message>()
        {
            new Message(){ Text = "You're standing on my scarf." },
            new Message(){ Text = "Would you like a jelly baby?" },
            new Message(){ Text = "To the rational mind, nothing is inexplicable; only unexplained." }
        };
    }
}

Test project

The test project (tests/RazorPagesProject.Tests/RazorPagesProject.Tests.csproj) includes xUnit, the ASP.NET Core testing infrastructure, and the Testcontainers MSSQL module:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="AngleSharp" Version="0.17.1" />
    <PackageReference Include="Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Identity.UI" Version="7.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="7.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="7.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="7.0.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>

    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.0" />

    <PackageReference Include="Testcontainers.MsSql" Version="3.0.0" />
    <PackageReference Include="xunit" Version="2.4.2" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\..\src\RazorPagesProject\RazorPagesProject.csproj" />
  </ItemGroup>

  <ItemGroup>
    <Content Update="xunit.runner.json">
      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
    </Content>
  </ItemGroup>

</Project>

The key dependencies are:

  • Microsoft.AspNetCore.Mvc.Testing - provides WebApplicationFactory for bootstrapping the app in tests
  • Microsoft.EntityFrameworkCore.SqlServer - the SQL Server database provider for Entity Framework Core
  • Testcontainers.MsSql - the Testcontainers module for Microsoft SQL Server

Existing SQLite-based test factory

The original project includes a CustomWebApplicationFactory that replaces the application's database with an in-memory SQLite instance:

public class CustomWebApplicationFactory<TProgram>
    : WebApplicationFactory<TProgram> where TProgram : class
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            var dbContextDescriptor = services.SingleOrDefault(
                d => d.ServiceType ==
                    typeof(DbContextOptions<ApplicationDbContext>));

            services.Remove(dbContextDescriptor);

            var dbConnectionDescriptor = services.SingleOrDefault(
                d => d.ServiceType ==
                    typeof(DbConnection));

            services.Remove(dbConnectionDescriptor);

            // Create open SqliteConnection so EF won't automatically close it.
            services.AddSingleton<DbConnection>(container =>
            {
                var connection = new SqliteConnection("DataSource=:memory:");
                connection.Open();

                return connection;
            });

            services.AddDbContext<ApplicationDbContext>((container, options) =>
            {
                var connection = container.GetRequiredService<DbConnection>();
                options.UseSqlite(connection);
            });
        });

        builder.UseEnvironment("Development");
    }
}

While this approach works, SQLite has behavioral differences from the database you'd use in production. In the next section, you'll replace it with a Testcontainers-managed Microsoft SQL Server instance.

Write tests with Testcontainers

The existing tests use an in-memory SQLite database. While convenient, this doesn't match production behavior. You can replace it with a real Microsoft SQL Server instance managed by Testcontainers.

Add dependencies

Change to the test project directory and add the SQL Server Entity Framework provider and the Testcontainers MSSQL module:

$ cd tests/RazorPagesProject.Tests
$ dotnet add package Microsoft.EntityFrameworkCore.SqlServer --version 7.0.0
$ dotnet add package Testcontainers.MsSql --version 3.0.0
Note

Testcontainers for .NET offers a range of modules that follow best practice configurations.

Create the test class

Create a MsSqlTests.cs file in the IntegrationTests directory. This class manages the SQL Server container lifecycle and contains a nested test class.

using System.Data.Common;
using System.Net;
using AngleSharp.Html.Dom;
using Microsoft.AspNetCore.Mvc.Testing;
using Microsoft.EntityFrameworkCore;
using RazorPagesProject.Data;
using RazorPagesProject.Tests.Helpers;
using Testcontainers.MsSql;
using Xunit;

namespace RazorPagesProject.Tests.IntegrationTests;

public sealed class MsSqlTests : IAsyncLifetime
{
    private readonly MsSqlContainer _msSqlContainer = new MsSqlBuilder().Build();

    public Task InitializeAsync()
    {
        return _msSqlContainer.StartAsync();
    }

    public Task DisposeAsync()
    {
        return _msSqlContainer.DisposeAsync().AsTask();
    }

    public sealed class IndexPageTests : IClassFixture<MsSqlTests>, IDisposable
    {
        private readonly WebApplicationFactory<Program> _webApplicationFactory;

        private readonly HttpClient _httpClient;

        public IndexPageTests(MsSqlTests fixture)
        {
            var clientOptions = new WebApplicationFactoryClientOptions();
            clientOptions.AllowAutoRedirect = false;

            _webApplicationFactory = new CustomWebApplicationFactory(fixture);
            _httpClient = _webApplicationFactory.CreateClient(clientOptions);
        }

        public void Dispose()
        {
            _webApplicationFactory.Dispose();
        }

        [Fact]
        public async Task Post_DeleteAllMessagesHandler_ReturnsRedirectToRoot()
        {
            // Arrange
            var defaultPage = await _httpClient.GetAsync("/")
                .ConfigureAwait(false);

            var document = await HtmlHelpers.GetDocumentAsync(defaultPage)
                .ConfigureAwait(false);

            // Act
            var form = (IHtmlFormElement)document.QuerySelector("form[id='messages']");
            var submitButton = (IHtmlButtonElement)document.QuerySelector("button[id='deleteAllBtn']");

            var response = await _httpClient.SendAsync(form, submitButton)
                .ConfigureAwait(false);

            // Assert
            Assert.Equal(HttpStatusCode.OK, defaultPage.StatusCode);
            Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
            Assert.Equal("/", response.Headers.Location.OriginalString);
        }

        private sealed class CustomWebApplicationFactory : WebApplicationFactory<Program>
        {
            private readonly string _connectionString;

            public CustomWebApplicationFactory(MsSqlTests fixture)
            {
                _connectionString = fixture._msSqlContainer.GetConnectionString();
            }

            protected override void ConfigureWebHost(IWebHostBuilder builder)
            {
                builder.ConfigureServices(services =>
                {
                    services.Remove(services.SingleOrDefault(service => typeof(DbContextOptions<ApplicationDbContext>) == service.ServiceType));
                    services.Remove(services.SingleOrDefault(service => typeof(DbConnection) == service.ServiceType));
                    services.AddDbContext<ApplicationDbContext>((_, option) => option.UseSqlServer(_connectionString));
                });
            }
        }
    }
}

Understand the test structure

Container lifecycle with IAsyncLifetime

The outer MsSqlTests class implements IAsyncLifetime. xUnit calls InitializeAsync() right after creating the class instance, which starts the SQL Server container. After all tests complete, DisposeAsync() stops and removes the container.

private readonly MsSqlContainer _msSqlContainer = new MsSqlBuilder().Build();

MsSqlBuilder().Build() creates a pre-configured Microsoft SQL Server container. Testcontainers modules follow best practices, so you don't need to configure ports, passwords, or startup wait strategies yourself.

Nested test class with IClassFixture

The IndexPageTests class is nested inside MsSqlTests and implements IClassFixture<MsSqlTests>. This gives the test class access to the container's private field and creates a clean hierarchy in the test explorer.

Custom WebApplicationFactory

Instead of using the SQLite-based factory, the nested CustomWebApplicationFactory retrieves the connection string from the running SQL Server container and passes it to UseSqlServer():

private sealed class CustomWebApplicationFactory : WebApplicationFactory<Program>
{
    private readonly string _connectionString;

    public CustomWebApplicationFactory(MsSqlTests fixture)
    {
        _connectionString = fixture._msSqlContainer.GetConnectionString();
    }

    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            services.Remove(services.SingleOrDefault(service => typeof(DbContextOptions<ApplicationDbContext>) == service.ServiceType));
            services.Remove(services.SingleOrDefault(service => typeof(DbConnection) == service.ServiceType));
            services.AddDbContext<ApplicationDbContext>((_, option) => option.UseSqlServer(_connectionString));
        });
    }
}

This factory:

  1. Removes the existing DbContextOptions<ApplicationDbContext> registration
  2. Removes the existing DbConnection registration
  3. Adds a new ApplicationDbContext configured with the SQL Server connection string from the Testcontainers-managed container
Note

The Microsoft SQL Server Docker image isn't compatible with ARM devices, such as Macs with Apple Silicon. You can use the SqlEdge module or Testcontainers Cloud as alternatives.

Run tests and next steps

Run the tests

Run the tests from the solution root:

$ dotnet test ./RazorPagesProject.sln

The first run may take longer because Docker needs to pull the Microsoft SQL Server image. On subsequent runs, the image is cached locally.

You should see xUnit discover and run the tests, including the MsSqlTests.IndexPageTests class. Testcontainers starts a SQL Server container, the tests execute against it, and the container is stopped and removed automatically after the tests finish.

Summary

By replacing SQLite with a Testcontainers-managed Microsoft SQL Server instance, the integration tests run against the same type of database used in production. This approach catches database-specific issues early, such as differences in SQL dialect, transaction behavior, or data type handling between SQLite and SQL Server.

The MsSqlTests class uses IAsyncLifetime to manage the container lifecycle, and a nested CustomWebApplicationFactory wires the container's connection string into the application's service configuration. You can apply this same pattern to any database or service that Testcontainers supports.

To learn more about Testcontainers, visit the Testcontainers overview.

Further reading