I am following this official tutorial.
Here is my code:

public sealed class CustomWebApplicationFactory : WebApplicationFactory<Program>
{
    private DbConnection _connection = null!; // <=========== B

    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        base.ConfigureWebHost(builder);

        builder.ConfigureTestServices(services =>
        {
            services.RemoveAll(typeof(DbContextOptions<AppDbContext>));
            services.RemoveAll(typeof(DbConnection));

            services.AddSingleton<DbConnection>(provider =>
            {
                var connection = new SqliteConnection("DataSource=:memory:");
                connection.Open();
                return connection;
            });

            services.AddDbContext<AppDbContext>((provider, options) =>
            {
                //options.UseSqlite(provider.GetRequiredService<DbConnection>()); // <=========== A
                options.UseSqlite(_connection); // <=========== B
            });

            var provider = services.BuildServiceProvider();
            _connection = provider.GetRequiredService<DbConnection>(); // <=========== B
        });
    }
}

There are two options:

• option A is based on the official tutorial but it produces error
  

  Message: 
  System.Net.Http.HttpRequestException : Response status code does not indicate success: 500 (Internal Server Error).
  Stack Trace: 
  HttpResponseMessage.EnsureSuccessStatusCode()
  HttpClientJsonExtensions.g__Core|12_0[TValue,TJsonOptions](HttpClient client, Task1 responseTask, Boolean usingResponseHeadersRead, CancellationTokenSource linkedCTS, Func4 deserializeMethod, TJsonOptions jsonOptions, CancellationToken cancellationToken)
  Gets.Should_return_ArrayOfUsers() line 10

• option B uses a field and it works.

What am I missing here? Why can’t we use SqliteConnection obtained from provider of AddDbContext()?