Add ReentrancyGuard status getter

CHANGELOG.md

@@ -123,6 +123,7 @@ With the new `ERC721Consecutive` extension, the internal workings of `ERC721` ar
  * `Initializable`: add a reinitializer modifier that enables the initialization of new modules, added to already initialized contracts through upgradeability. ([#3232](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3232))
  * `Initializable`: add an Initialized event that tracks initialized version numbers. ([#3294](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3294))
  * `ERC2981`: make `royaltyInfo` public to allow super call in overrides. ([#3305](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3305))
+ * `ReentrancyGuard`: Add a `_reentrancyGuardStatus` function to expose the guard status. ([#3713](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3713))
 
 ### Upgradeability notice
 

contracts/mocks/ReentrancyMock.sol

@@ -35,6 +35,8 @@ contract ReentrancyMock is ReentrancyGuard {
         _count();
         bytes4 func = bytes4(keccak256("callback()"));
         attacker.callSender(func);
+
+        require(_reentrancyGuardStatus() == 2, "ReentrancyMock: _reentrancyGuardStatus failed");
     }
 
     function _count() private {

contracts/security/ReentrancyGuard.sol

@@ -66,4 +66,11 @@ abstract contract ReentrancyGuard {
         // https://eips.ethereum.org/EIPS/eip-2200)
         _status = _NOT_ENTERED;
     }
+
+    /**
+     * expose _status as internal function, the caller decides what to do with it
+     */
+    function _reentrancyGuardStatus() internal view returns (uint256) {
+        return _status;
+    }
 }