[Minor] Tests: backup version with SP500 futures

Signed-off-by: oleg komarov <o.komarov11@imperial.ac.uk>
[Fix] loadresults: concatenation bug

Signed-off-by: oleg komarov <o.komarov11@imperial.ac.uk>
[Change] Test: using SPY (etf) instead of SPX (fut)

Signed-off-by: oleg komarov <o.komarov11@imperial.ac.uk>