app/code/Magento/Payment/Gateway/Command/CommandPool.php

app/code/Magento/Payment/Gateway/Config/ValueHandlerPool.php

...code/Magento/Payment/Gateway/Request/BuilderComposite.php

app/code/Magento/Payment/Gateway/Response/HandlerChain.php

.../Magento/Payment/Gateway/Validator/ValidatorComposite.php

app/code/Magento/Payment/Gateway/Validator/ValidatorPool.php

app/code/Magento/Payment/Model/Method/Logger.php

...nto/Payment/Test/Unit/Gateway/Command/CommandPoolTest.php

...Payment/Test/Unit/Gateway/Config/ValueHandlerPoolTest.php

...ayment/Test/Unit/Gateway/Request/BuilderCompositeTest.php

...o/Payment/Test/Unit/Gateway/Response/HandlerChainTest.php

...nt/Test/Unit/Gateway/Validator/ValidatorCompositeTest.php

...Payment/Test/Unit/Gateway/Validator/ValidatorPoolTest.php

...ode/Magento/Payment/Test/Unit/Model/Method/LoggerTest.php