Function apply 

pub fn apply(
    harness: &Harness,
    dialect: &str,
    url: &str,
    plan: bool,
    fleet: bool,
    tenant: Option<&str>,
    strict: bool,
) -> Result<(), String>

Applies the harness’s migrations to the database at url; with fleet or plan, reconciles the tenants registered in the control database at url instead.

Errors

A human-readable message when the dialect is unsupported, the flags contradict each other, the binary lacks the postgres feature, the server is unreachable, or a migration fails. In strict mode any degraded tenant is one.