FixEntryAssembly.cs

private static void FixEntryAssembly()
{
    // http://dejanstojanovic.net/aspnet/2015/january/set-entry-assembly-in-unit-testing-methods/
    AppDomainManager manager = new AppDomainManager();
    FieldInfo entryAssemblyfield = manager.GetType()
        .GetField("m_entryAssembly", BindingFlags.Instance | BindingFlags.NonPublic);
    entryAssemblyfield?.SetValue(manager, typeof(Startup).Assembly);

    AppDomain domain = AppDomain.CurrentDomain;
    FieldInfo domainManagerField = domain.GetType()
        .GetField("_domainManager", BindingFlags.Instance | BindingFlags.NonPublic);
    domainManagerField?.SetValue(domain, manager);
}