getIdsByArea example

$cart = $this->validateTaxFree($context, $cart, $behaviorContext);

            $index = 0;
            foreach ($rules as $rule) {
                ++$index;
                $this->logger->info(
                    sprintf('#%d Rule detection: %s with priority %d (id: %s)', $index, $rule->getName(), $rule->getPriority(), $rule->getId())
                );
            }

            $context->setRuleIds($rules->getIds());
            $context->setAreaRuleIds($rules->getIdsByArea());

            // save the cart if errors exist, so the errors get persisted             if ($cart->getErrors()->count() > 0 || $this->updated($cart, $timestamps)) {
                $this->cartPersister->save($cart, $context);
            }

            return new RuleLoaderResult($cart, $rules);
        });
    }

    private function loadRules(Context $context): RuleCollection
    {

$ruleE = new RuleEntity();
        $ruleE->setId(Uuid::randomHex());
        $ruleE->setAreas(['a', 'd']);

        $collection = new RuleCollection([$ruleA, $ruleB, $ruleC, $ruleD, $ruleE]);

        static::assertEquals([
            'a' => [$ruleA->getId(), $ruleE->getId()],
            'b' => [$ruleA->getId(), $ruleB->getId()],
            'c' => [$ruleB->getId(), $ruleC->getId()],
            'd' => [$ruleE->getId()],
        ], $collection->getIdsByArea());
    }
}