perMonth example

        $this->assertEquals($rate, Rate::fromString((string) $rate));
    }

    public static function provideRate(): iterable
    {
        yield [new Rate(new \DateInterval('PT15S'), 10)];
        yield [Rate::perSecond(10)];
        yield [Rate::perMinute(10)];
        yield [Rate::perHour(10)];
        yield [Rate::perDay(10)];
        yield [Rate::perMonth(10)];
        yield [Rate::perYear(10)];
    }
}