spot check; snap inspection; surprise test
An unannounced inspection or test conducted without prior warning. Often used in workplace, school, or regulatory contexts.
See also: 抜き打ち検査 (ぬきうちけんさ)
A spot check was conducted and all the documents were inspected.
先生が抜き打ち調査として小テストをした。
The teacher gave a surprise quiz as a spot check.
Very similar in meaning; 検査 is more about inspection/examination, while 調査 leans toward investigation/survey. Often interchangeable.
Compound of 抜き打ち (ぬきうち, 'surprise, without warning') and 調査 (ちょうさ, 'investigation, survey').