Way to test IP proxies

I want to test a proxy [gateway] service. What might be a simplest way to check proxies IP speed, quality [not being banned by data aggregators and providers like Google, Facebook], and other parameters)?

• Any hints to a script?
• Any proxy test benchmark?

What I know so far:

import urllib.request
import time
opener = urllib.request.build_opener(
    urllib.request.ProxyHandler(
         {'http': 'http://127.0.0.1:9999'}))
start =  time.time()
print(opener.open('http://example.com').read())
print ('total time: {0}'.format(time.time()-start))