Testing with InMemory

[rowanmiller]

The most important thing is how to scope the database to a single test...

using Microsoft.Data.Entity;
using Microsoft.Data.Entity.Infrastructure;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Linq;

namespace ConsoleApp1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var serviceCollection = new ServiceCollection();
            serviceCollection
                .AddEntityFramework()
                .AddInMemoryDatabase()
                .AddDbContext<SampleContext>(c => c.UseInMemoryDatabase());


            using (var db = serviceCollection.BuildServiceProvider().GetService<SampleContext>())
            {
                db.Blogs.Add(new Blog { Url = "Test" });
                db.SaveChanges();
                Console.WriteLine(db.Blogs.Count());
            }

            using (var db = serviceCollection.BuildServiceProvider().GetService<SampleContext>())
            {
                db.Blogs.Add(new Blog { Url = "Test" });
                db.SaveChanges();
                Console.WriteLine(db.Blogs.Count());
            }
        }
    }

    public class SampleContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
    }

    public class Blog
    {
        public int BlogId { get; set; }
        public string Url { get; set; }
    }
}

[rowanmiller]

Should also cover this point that was mentioned in #105

Keep DbContext's isolated; don't re-use the same context to seed the database and then query.

[VeronicaWasson]

I'm trying to write a test that uses two DbContext's, sharing the same in-memory DB. The idea is to create the entities using the first context, and pass a clean context to the code that I'm testing. That way I can validate that I'm loading navigation properties correctly, etc, in my EF7 code. The best I could find was to register my DbContext as a transient:

public class TestClass
{
    private readonly ServiceCollection _serviceCollection;
    private readonly DbContextOptions<MyDbContext> _options;

    public TestClass()
    {
        var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>();
        optionsBuilder.UseInMemoryDatabase();
        _options = optionsBuilder.Options;

        var _serviceCollection = new ServiceCollection();
        _serviceCollection
            .AddEntityFramework()
            .AddInMemoryDatabase();

        _serviceCollection.AddTransient<MyDbContext>(provider => new MyDbContext(provider, _options));
    }

    [Fact]
    public Test1()
    {
        IServiceProvider provider = _serviceCollection.BuildServiceProvider();
        using (var context = provider.GetService<MyDbContext>())
        {
            context.Add(new Thing { Id = 1 });
            context.SaveChanges();
        }

        using (var context = provider.GetService<ApplicationDbContext>())
        {
            // test with a new context but same DB
        }
    }
}

It seems to work, but is there a better way to achieve this?

[rowanmiller]

@MikeWasson it's a bit of a "level up" on DI skills... but you can create scopes within a service provider to get new instances of scoped services... but the non-scoped services (such as the InMemory store) are shared between all scopes on the provider.

This actually emulates nicely what happens in ASP.NET - where a new scope is created for each request. So Test1() now approximates some data being inserted on one request and then some other logic happening on a second request that accesses the same database.

public class TestClass
{
    private readonly ServiceCollection _serviceCollection;

    public TestClass()
    {
        _serviceCollection = new ServiceCollection();
        _serviceCollection
            .AddEntityFramework()
            .AddInMemoryDatabase()
            .AddDbContext<SampleContext>(c => c.UseInMemoryDatabase());
    }

    [Fact]
    public Test1()
    {
        IServiceProvider provider = _serviceCollection.BuildServiceProvider();
        using (var scope = provider.GetRequiredService<IServiceScopeFactory>().CreateScope())
        {
            var context = scope.ServiceProvider.GetService<MyDbContext>())
            context.Add(new Thing { Id = 1 });
            context.SaveChanges();
        }

        using (var scope = provider.GetRequiredService<IServiceScopeFactory>().CreateScope())
        {
            var context = scope.ServiceProvider.GetService<MyDbContext>())
            // test with a new context but same DB
        }
    }
}

[rowanmiller]

Page is now available at http://docs.efproject.net/en/latest/miscellaneous/testing.html

@MikeWasson I came up with some patterns to make things a little simpler (though we still have plenty of room for improvement - mostly implementing dotnet/efcore#3253) so you should take a look at the final article.