You might want to have a cell just for __future__ imports, but there are no restrictions

class Tree[source]

Tree(left:Tree, right:Tree)

These cells just run like normal when testing with nbdev_test_nbs

assert Tree(Tree(None,None),None) is not None

You can use special comments to export a cell containing __future__ imports

If you see SyntaxError: from __future__ imports must occur at the beginning of the file:

%nbdev_export
from __future__ import annotations

you'll need to move the __future__ import to the top of the cell:

from __future__ import annotations
%nbdev_export

# from decision_tree.test.from_future import *
# Tree(Tree(None,None),None), annotations