We are implementing a new credit card processor (software platform that manages all the processing of credit cards) and want to conduct a pilot in production environment (after being certify in test environment). The objective of the pilot is to make sure that the processor works OK in production as it did in the certification environment. We do not want to repeat 100% of the tests made in the certification phase but only those we consider to have more impact on customers, for example ATM cash advance transactions and POS purchase transactions.
We want to know how to calculate the size of the test group that will participate in the pilot? How many times one specific test has to be repeated to be considered OK, for example: if one test is an ATM withdraw, how many tests should be done?