Distribution

Checking the distribution

A property can pass vacuously if its generators never reach the interesting inputs. Classify records labels per run; after a fully passing property the runner prints the share of runs that hit each label.

#[Property(runs: 500)]
public function holds(int $n): void
{
    Classify::when($n === 0, 'zero');
    Classify::label($n % 2 === 0 ? 'even' : 'odd');
    // ... assertions ...
}
// Property "holds" distribution: odd 51% (255/500), even 49% (245/500), zero 1% (3/500)

A label recorded several times within one run still counts once for that run.

Enforcing the distribution

Classify::cover() upgrades the printed hint to a hard requirement: the label must occur in at least the given percentage of passing runs, or the property fails with a CoverageViolationException — even though every run passed. Use it to make vacuous passes impossible in CI.

#[Property(runs: 500)]
public function holds(int $n): void
{
    Classify::cover($n % 2 === 0, 'even', 30.0); // fail if < 30% of runs are even
    // ... assertions ...
}

Discarded attempts (Assume::that()) are excluded from the denominator and replaced until all requested successful runs complete. Exceeding maxDiscards fails with GaveUpException (see Assume::that()).