這是什麼樣的英文用法?

This toy is suitable for children above 5 and it did pass the safety test.

"did" in the above sentence is the past tense of the auxiliary verb "do", which is used to emphasize the main verb "passed" in the original sentence.

** original sentence : it passed the safety test
~ negative sentence: it did not pass the safety test
~ emphasizing positive sentence: it did pass the safety test 它 "確實" 通過了安全測試

兩個句型 文法上都是對的. 只是 did 有著重強調(加強)後面那個動詞的意思.
He passed the exam - 他通過了考試.
He did pass the exam - 他是真的通過了考試