TestClassBase.cs

public abstract class TestClassBase
{
    private readonly IContainer _container 
        = Root.Container.GetNestedContainer();

    protected T GetInstance<T>()
    {
        return _container.GetInstance<T>();
    }

    protected void Inject<T>(T instance)
    {
        _container.Configure(cfg => cfg.For<T>().Use(instance));
    }
}