In Spanish, El Futuro Simple and El Futuro Perfecto can be used to express either surprise, rejection or suspicion to something that someone has said, or to someone's attitude.
Ese hombre me ha empujado al pasar por mi lado, ¡será grosero!That man pushed me when he walked past me, isn't he rude?
-Voy a ir a una playa nudista. -¡No serás capaz!-I am going to go to a nudist beach. -You won't!/You won't dare!
In the first example, the speaker is expressing "rejection/disapproval" to the man's attitude. The second example is a reaction to what the first speaker just said. This reaction could be taken as "surprise", because she doesn't think her friend capable of doing that, or a "rejection/disapproval" to the idea of her friend going to a nudist beach.
When we use El Futuro Simple, we are referring to actions related to the present (or recent past) or the future.
-Ayer puse la maleta de mi novio en la calle. -¡No habrás sido capaz!-Yesterday I put my boyfriend's suitcase in the street. -You didn't! /I can't believe you did that!
-Me faltan 20 euros. ¡No los habrás cogido tú!-I'm missing 20 euros. You didn't take them, did you?
The first example is shows the speaker's surprise as to her friend's actions. In the second example the speaker is expressing suspicion.
Both cases refer to past actions.
See also Using El Futuro simple or El Futuro Perfecto to express objection/disbelief to a statement said before
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