be tested time and again and proved fight; it has proved effective (/it comes out right) every time; put to repeated tests and proved satisfactory
? 這種新殺蟲藥效果良好，～。This new insecticide has proved effective every time it is used.
屢試不爽lǚ shì bù shuǎnɡ
爽：差錯。多次試驗都沒有差錯。time-tested, it comes out right every time, put to repeated tests and prove right