Tried and tested/trusted - Idioms by The Free Dictionary
tried and tested/trusted
tried and tested
Proven to be reliable through frequent, widespread, or long-time use. The tried and tested method for getting someone to confess is to just let them keep talking. The tried and tested first food for babies is rice cereal, but you can really feed them anything mushy.
ˌtried and ˈtested/ˈtrusted (British English) (American English ˌtried and ˈtrue) that you have used or relied on in the past successfully: We’ll be using a tried and tested technique to solve the problem.