The first phase of any backtesting exercise is the hypothesis specification and the determined time and ressource investment to properly test this hypothesis.
The second phase of a backtesting exercise is to investigate quality of data. That by itself can be a tedious stask which is nevertheless necessary.
The 3rd phase consists of the hands on programer getting locked into the exercise in which cost of strategy along with proper simulation are performed.
Before potential deployment, it is important to analyse to what extend the results of the backtest correspond to the hypothesis from first phase.