Fair use copying, in any amount so deemed, "is not an infringement of copyright". The statute lists four tests. Any one of these, or other conditions, may be sufficient.

The third test is "the amount and substantiality of the portion used in relation to the copyrighted work as a whole".

https://www.law.cornell.edu/uscode/text/17/107

Again, Hagemeister establishes that a bare minimum copying is performed, sufficient to verify code function. A fact which would overwhelmingly tend to a fair use finding.