> テスト中に私の携帯が鳴ってしまった。

Means: My phone accidentally rang during the test.

Can someone explain why the particle に is required after the 中?

Why does: テスト中私の携帯が鳴ってしまった。

Not work here?
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2022-02-01T19:01:19.703
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particle-に
中に vs 中 - When to use に. テスト中に私の携帯が鳴ってしまった
Here に is an article used with time. In spoken Japanese, it can be considered
obvious and dropped completely. In spoken Japanese, it would be replaced with
a pause, or, if writing out spoken Japanese, with a comma to indicate the
pause.テスト中、私の携帯が鳴ってしまった。
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2022-02-01T20:28:55.277
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answer
テスト中 **に** sounds more natural than テスト中 (without に) in this sentence.

This is because the phone ringing is something that happened at a specific
point during the exam. に has the effect of putting focus on that specific
point of time. テスト中 (without に) sounds a bit incomplete and vague.

Though the difference may not be so obvious as with 間, these are related.

  * [In this particular sentence is 間 and 間に interchangeable?](https://japanese.stackexchange.com/q/55254/43676)
  * [Difference between 間 and 間に](https://japanese.stackexchange.com/q/12539/43676)
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answer