19 files declare their use of BillingPeriod in Commerce Recurring Framework 8

BillingPeriodItem.php in src/Plugin/Field/FieldType/BillingPeriodItem.php

BillingPeriodItemTest.php in tests/src/Kernel/BillingPeriodItemTest.php

BillingPeriodTest.php in tests/src/Kernel/BillingPeriodTest.php

BillingScheduleInterface.php in src/Plugin/Commerce/BillingSchedule/BillingScheduleInterface.php

ChargeTest.php in tests/src/Kernel/ChargeTest.php

Fixed.php in src/Plugin/Commerce/BillingSchedule/Fixed.php

FullPrice.php in src/Plugin/Commerce/Prorater/FullPrice.php

IntervalBase.php in src/Plugin/Commerce/BillingSchedule/IntervalBase.php

ProductVariationTest.php in tests/src/Kernel/Plugin/Commerce/SubscriptionType/ProductVariationTest.php

Proportional.php in src/Plugin/Commerce/Prorater/Proportional.php

ProportionalTest.php in tests/src/Kernel/Plugin/Commerce/Prorater/ProportionalTest.php

ProraterBase.php in src/Plugin/Commerce/Prorater/ProraterBase.php

ProraterInterface.php in src/Plugin/Commerce/Prorater/ProraterInterface.php

RecurringOrderManagerTest.php in tests/src/Kernel/RecurringOrderManagerTest.php

Rolling.php in src/Plugin/Commerce/BillingSchedule/Rolling.php

StandaloneTest.php in tests/src/Kernel/Plugin/Commerce/SubscriptionType/StandaloneTest.php

SubscriptionTest.php in tests/src/Kernel/Entity/SubscriptionTest.php

SubscriptionTypeBase.php in src/Plugin/Commerce/SubscriptionType/SubscriptionTypeBase.php

SubscriptionTypeInterface.php in src/Plugin/Commerce/SubscriptionType/SubscriptionTypeInterface.php