run you strategy over some data. you can get history from quandl.
here's a world class winner. if the previous day was up: buy the open sell the close
import pandas as pd
import numpy as np
import Quandl
df=Quandl.Quandl.get('GOOG/NYSE_SPY',authtoken=QUANDLTOKEN,sort_order='desc')
df['upday']=...