Function coverage_from_rules 

pub fn coverage_from_rules(
    rules: &[Rule],
    group_by: CoverageGroup,
) -> Result<CoverageReport>

Group the rules by group_by.

A rule counts as enabled only when enabled is true. Each rule adds at most one to a group, and a rule with no key adds one to unmapped_rules. A missing or null field yields no key; a present field of the wrong type is kind http. Only the fields the grouping reads are checked.