Function testable_random_sample 

pub fn testable_random_sample() -> NHSNumber

Generate a NHS Number testable range random sample. The generated number is valid but is never going to be issued.

Example:

use nhs_number::{NHSNumber, testable::*};
let nhs_number = testable_random_sample();
assert!(nhs_number >= *TESTABLE_MIN);
assert!(nhs_number <= *TESTABLE_MAX);