Function check_spec 

pub fn check_spec(spec: &Spec, lex_source: &str, trials: u32) -> CheckResult

Check a spec against a Lex program. The program must define the function the spec refers to (by name).

trials: number of random samples for the randomized strategy. Recommended ≥ 1000 for honest “proved” claims; small numbers (e.g. 10) are useful for fast smoke tests.