change manager unit test to use guzzle mock response
change manager unit test to use guzzle mock response

sphereio/sphere-php-sdk,sphereio/commercetools-php-sdk,sphereio/commercetools-php-sdk,sphereio/commercetools-php-sdk,sphereio/sphere-php-sdk,sphereio/commercetools-php-sdk,sphereio/sphere-php-sdk,sphereio/sphere-php-sdk