Future perfect progressive tense indicates an ongoing event that will be completed by a certain point in the future.
- The party will have been going for ages by the time we arrive.
- In just half an hour from now, we will have been working for 14 hours straight.
The pattern for forming future perfect progressive tense is as follows:
- Will have been + present participle
To form the negative, place not between the auxiliaries will and have. To form a question, move will to the beginning of the sentence, in front of the subject.
- They will have been preparing the food.
- Will they have been preparing the food?
- They will not have been preparing the food.