屡试不爽

屢試不爽
lǚshìbùshuǎng
  1. well-tried
  2. time-tested

CEDICT

to prove effective every time

Wiktionary

屡次试验，结果都相同。

重編國語辭典

反覆试验都没有差错，比喻每次都成功

維基詞典

Entry Composition

1 屡 lǚ
  1. time and again
  2. repeatedly
  3. frequently
2 试 shì
  1. to test
  2. to try
  3. experiment
  4. examination
  5. test
3 不爽 bùshuǎng
  1. not well
  2. out of sorts
  3. in a bad mood
  4. without discrepancy
  5. accurate

Related entries

磨难 mónàn
  1. a torment
  2. a trial
  3. tribulation
  4. a cross (to bear)
  5. well-tried