subjunctive mood or not

(Not a Teacher)

Both A and B could work.

I agree with SlickVic that both A and B are possible. There is no verb in the subjunctive mood in that sentence.

Does it mean that the answer depends on the situation? For example, if "you" took the exam for the second time yesterday, then "a" is proper; if "you" didn't take the exam but you feel you should have taken the exam, then "b" can be used to comfort or explain to "you" that you didn't need to?

5jj said:

You needn't have taken the examination again since you had already passed it. You took the examination.
You didn't need to take the examination again since you had already passed it. You may or may not have taken it. We don't know. Only more context will tell us.

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Thank 5jj for the explanation. I'm still wondering if in the second condition, "you may have taken it", then shouldn't "I" say "you needn't have taken..."?
Only when we comment on something that did not happen or has not happen can we say didn't neet to or don't need to? LIke in the sentence You don't need to take the examination since you have already passed it.
Is this understanding correct?

You didn't need to take the examination again, so why did you do it? You took it.
You didn't need to take the examination again, which is why I didn't enter you. You didn't take it.

5jj said:

You didn't need to take the examination again, so why did you do it? You didn't need to take the examination again, which is why I didn't enter you. You didn't take it.

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So when You took it, both two sentences can be used, 1. You didn't need to take...
2. You needn't have taken
I feel confused because we were taught that "didn't need to" is used to refer to something that did not happen while "needn't have done" refers to something that had happened but actually there was no such a necessity.
But in fact they can be used to expressed the same situation?

chance22 said:

So when You took it, both two sentences can be used, 1. You didn't need to take...
2. You needn't have taken
I feel confused because we were taught that "didn't need to" is used to refer to something that did not happen while "needn't have done" refers to something that had happen but actually is not needed.
But in fact they can be used to expressed the same situation?

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You can keep asking, but the answer won't change.

Guest: Oh, I forget to confirm my booking!
Hotel manager: That's OK. You didn't need to.

Guest: I confirmed my booking yesterday.
Hotel manager: Thank you. But you didn't need to. (You needn't have done it)

Whether Guest needed to confirm the booking is not dependent on whether he actually did so.

Raymott said:

Guest: I confirmed my booking yesterday.
Hotel manager: Thank you. But you didn't need to. (You needn't have done it)

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OK I got it from the above example--both can be used in this situation
Thank you very much!

I agree with everything said but would add that Americans are less likely to say "you needn't have" than "you didn't need to."