Improve role behavior tests (#1300)
Improve role behavior tests (#1300)

* The public role behavior now also tests the modifer.

* Fixed linter error.

OpenZeppelin/openzeppelin-contracts,OpenZeppelin/zep-solidity,OpenZeppelin/zeppelin-solidity,OpenZeppelin/zep-solidity,OpenZeppelin/zeppelin-solidity,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/openzeppelin-contracts