Learn English – Negative forms “don’t have” vs. “have not”

Those constructions are natural and idiomatic.

However, for me, the first example,

I wouldn't have told you if I weren't going to tell you.

required me to reread it, since I initially parsed the sentence with:

to tell <somebody> <something>

instead of

to tell <somebody>.

By rearranging the parts of that phrase, it gets rid of that confusion;

If I weren't going to tell you, I wouldn't have told you.

You can similarly change positive "would have" statements into questions.

So,

If it had been sunny yesterday, he would have gone to the movies.

and

He would have gone to the movies if it had been sunny yesterday.

can be transformed into:

Would he have gone to the movies if it had been sunny yesterday?

The standard way is to clarify your answer by rephrasing the question rather than only saying "no" or "yes".

A - This is not a duplicate question.
B - Yes, it is [a duplicate question].

A - This is not a duplicate question.
B - No, it is not [a duplicate question].