What is the difference between test results of strategy tester and live accounts

What there are different results. Just  because of trading conditions.

It depends on Metatrader (MT4 or MT5).

I am suggesting to read this summary thread:
All (not yet) about Strategy Tester, Optimization and Cloud
Becuase of missing ticks in history, slippage, network connection and spread. Allso requotes if you have a marketmaker broker.