Замените сервис на макет с помощью WebApplicationFactory

Question

Я пытаюсь заменить реализацию IMessageFormatter на MockMessageFormatter для теста.

public class MyMockingWebApplicationFactory<TStartUp> : WebApplicationFactory<Startup>
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services => { services.AddTransient<IMessageFormatter, MockMessageFormatter>(); });
    }
}

Тест выглядит так:

public class MockingTests : IClassFixture<MyMockingWebApplicationFactory<Startup>>
{
    public MockingTests(MyMockingWebApplicationFactory<Startup> webApplicationFactory)
    {
        _webApplicationFactory = webApplicationFactory;
    }

    private readonly MyMockingWebApplicationFactory<Startup> _webApplicationFactory;

    [Fact]
    public async Task MockIt()
    {
        var client = _webApplicationFactory.WithWebHostBuilder(builder =>
        {
            //builder.ConfigureServices(services =>
            //{
            //    var foo = ServiceDescriptor.Transient<IMessageFormatter, MessageFormatter>();
            //    services.Remove(foo);
            //    services.AddTransient<IMessageFormatter, MockMessageFormatter>();
            //});
        }).CreateClient();

        var message = "Hello";
        var expectedReversedMessage = "foo";
        var result = await client.GetAsync($"/?message={message}");
        var content = await result.Content.ReadAsStreamAsync();
        var htmlParser = new HtmlParser();
        var htmlDocument = await htmlParser.ParseAsync(content);
        var messageElement = htmlDocument.GetElementById("original-message");
        var reversedMessageElement = htmlDocument.GetElementById("reversed-message");
        Assert.Equal(message, messageElement.InnerHtml);
        var reversedMessage = reversedMessageElement.InnerHtml;
        Assert.Equal(expectedReversedMessage, reversedMessage);
    }
}

I 'мы пытались добавить вызов к ConfigureServices в клиенте и в MyMockingWebApplicationFactory, но проблема, похоже, в том, что класс real Startup выполняется после регистрации теста и поэтому перезаписывает их.

Класс real StartUp:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); ;
        services.AddTransient<IMessageFormatter, MessageFormatter>();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        app.UseDeveloperExceptionPage();
        app.UseMvc();
    }
}

Answer 1

замените ваш код:

builder.ConfigureServices(services => { services.AddTransient<IMessageFormatter, MockMessageFormatter>(); });

на:

builder.ConfigureTestServices(services =>
        {
            var serviceProvider = services.BuildServiceProvider();
            var descriptor =
                new ServiceDescriptor(
                    typeof(IMessageFormatter),
                    typeof(MockMessageFormatter),
                    ServiceLifetime.Transient);
            services.Replace(descriptor);
        });