The OP's example ( is-positive-integer) has tests, and is only three lines long, and is on major release version 3.X, because despite all that, it had serious problems in versions 1 and 2.
"Serious problems in versions 1 and 2" suggests that it might be a good idea not to write your own version 1.
But to be explicit about the history: version one[0] had dependencies. Version two[1] had no dependencies, and a comment on github suggests that it might be wrong but I can't immediately see how. Version three[2] is a different implementation, and adds another export.
