Create a prototype to start playtesting! It will be rough, rocky, drafty and incomplete. We know!
It could be
* A very short story with one or two choices in twine/Inform 7
* A paper prototype (STRONGLY RECOMMENDED)
https://www.gdcvault.com/play/1020509/Paper-Tales-A-Guide-to (Links to an external site.)
* or something else? Role playing?