There are a lot of things to consider when choosing how many samples you need for testing. Please consider these factors when deciding your sample size for data collection.
1) Statistics – you can’t logically argue with it…
2) Available parts and materials
3) Cost of samples
4) Time allowance for the testing
5) Other peoples' time (line time)
6) Industry standards
7) Your confidence level
8) Available equipment and capacity
9) Spare samples, to compensate for lost/damaged samples
10) Make sure you at very least have three data points