By testing electronic voting machines, officials need to use the same machines for the actual voting process. Strict controls need to be implemented to ensure that the same machines are used on voting day to avoid any issues of efficiency or transparency. Luckily, such a safeguard system wouldn't be hard to implement.
No, there is not a method in place to make sure that the electronic voting machines are identical to the ones tested, because there are too many people involved in the voting process, that have supervision over too many machines. There is no way that those in charge can audit every single machine in order to make sure that there is no fraud. The system is too large to monitor.