Startup.cs

namespace blackdunes.chronicles
{
    public class Startup
    {
        private readonly IHostingEnvironment env;

        public Startup(IHostingEnvironment env)
        {
            // Set up configuration sources.
            var builder = new ConfigurationBuilder()
                .AddJsonFile("appsettings.json", optional: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

            if (env.IsDevelopment())
            {
                // For more details on using the user secret store see http://go.microsoft.com/fwlink/?LinkID=532709
                builder.AddUserSecrets();
            }

            builder.AddEnvironmentVariables();
            Configuration = builder.Build();
            this.env = env;
        }

        public IConfigurationRoot Configuration { get; set; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
              // Add EntityFramework,  but if my tests have already defined it,  then use what they have defined instead.
              services.AddEntityFramework()
                  .AddNpgsql()
                  .AddDbContext<ApplicationDbContext>(options => 
                      options.UseNpgsql(Configuration["Data:DefaultConnection:ConnectionString"]));

            
            services.AddMvc();

            services.AddScoped<IChronicleRepository, ChronicleRepository>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env,
            ILoggerFactory loggerFactory, ContextSeedData data)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            app.UseStaticFiles();

            Mapper.Initialize(config =>
            {
                config.CreateMap<Child, ChildViewModel>().ReverseMap();
            });

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }

        // Entry point for the application.
        public static void Main(string[] args) => WebApplication.Run<Startup>(args);
    }

Test.cs

      [Fact]
      public async Task Can_Setup_Whole_Server() {
        var server = new TestServer(
            TestServer.CreateBuilder()
              .UseEnvironment("Testing")
              .UseServices(services => {
                services.AddEntityFramework()
                  .AddInMemoryDatabase()
                  .AddDbContext<ApplicationDbContext>(options => 
                      { 
                        options.UseInMemoryDatabase(); options.Lock();
                      });
                }).UseStartup<Startup>());

        await Task.Yield();

        server.CreateClient().PostAsync("/api/children",
            new System.Net.Http.StringContent("{ Name: 'Alistair', FamilyName: 'B', Sex: 'Male', DateOfBirth: '2015-01-01' }",
              new System.Text.UTF8Encoding(), "application/json")).Wait();
        
        var response = await server.CreateClient().GetAsync("/api/children");
        var body = await response.Content.ReadAsStringAsync();
        body.Should().Contain("A");
      }