XUnit DI through overridden Startup file (.net core)

I have build a WebAPI and apart from my tests running on Postman I would like to implement some Integration/Unit tests.

Now my business logic is very thin, most of the time its more of CRUD actions, therefore I wanted to start with testing my Controllers.

I have a basic setup. Repository pattern (interfaces), Services (business logic) and Controllers. The flow goes Controller (DI Service) -> Service (DI Repo) -> Repo Action!

So what I did was override my Startup file to change into a in memory database and the rest should be fine (I would assume) Services are added, repos are added and now I am pointing into a in memory DB which is fine for my basic testing.

namespace API.UnitTests
{    
    public class TestStartup : Startup
    {
        public TestStartup(IHostingEnvironment env)
            : base(env)
        {

        }

        public void ConfigureTestServices(IServiceCollection services)
        {
            base.ConfigureServices(services);
            //services.Replace<IService, IMockedService>();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            base.Configure(app, env, loggerFactory);
        }

        public override void SetUpDataBase(IServiceCollection services)
        {
            var connectionStringBuilder = new SqliteConnectionStringBuilder { DataSource = ":memory:" };
            var connectionString = connectionStringBuilder.ToString();
            var connection = new SqliteConnection(connectionString);

            services
                .AddEntityFrameworkSqlite()
                .AddDbContext<ApplicationDbContext>(
                    options => options.UseSqlite(connection)
                );
        }
    }
}

I wrote my first test, but the DatasourceService is not there:

The following constructor parameters did not have matching fixture data: DatasourceService datasourceService

namespace API.UnitTests
{
    public class DatasourceControllerTest
    {
        private readonly DatasourceService _datasourceService; 

        public DatasourceControllerTest(DatasourceService datasourceService)
        { 
            _datasourceService = datasourceService;            
        }

        [Xunit.Theory,
        InlineData(1)]
        public void GetAll(int companyFk) {
            Assert.NotEmpty(_datasourceService.GetAll(companyFk));
        }
    }
}

What am I missing?