Thaney, K. (2020, April 8). Open Infrastructure in times of crisis: How IOI can help. Invest in Open Infrastructure. https://investinopen.org/2020/04/08/open-infrastructure-in-times-of-crisis.html

According to this checklist, a User Story should be:

Indepedent (of all others)

Negociable (not a specific contract for features)

Valuable (or vertical)

Estimable (to a good approximation)

Small (so as to fit within an iteration)

Testable (in principle, even if there isn't a test for it yet)

Source(s):

1. Glossary: INVEST - Agile Alliance
2. INVEST at XP 1-2-3 by Bill Wake