Improved bounty tests. (#1350)

* Improved bounty tests.

* Fixed linter errors.

* Addressed review comments.

contracts/mocks/BreakInvariantBountyMock.sol

@@ -5,14 +5,24 @@ pragma solidity ^0.4.24;
 // solium-disable-next-line max-len
 import {BreakInvariantBounty, Target} from "../bounties/BreakInvariantBounty.sol";
 
-contract SecureInvariantTargetMock is Target {
-  function checkInvariant() public returns(bool) {
+contract TargetMock is Target {
+  bool private exploited;
+
+  function exploitVulnerability() public {
+    exploited = true;
+  }
+
+  function checkInvariant() public returns (bool) {
+    if (exploited) {
+      return false;
+    }
+
     return true;
   }
 }
 
-contract SecureInvariantTargetBounty is BreakInvariantBounty {
+contract BreakInvariantBountyMock is BreakInvariantBounty {
   function _deployContract() internal returns (address) {
-    return new SecureInvariantTargetMock();
+    return new TargetMock();
   }
 }

contracts/mocks/InsecureInvariantTargetBounty.sol

@@ -1,18 +0,0 @@
-pragma solidity ^0.4.24;
-
-// When this line is split, truffle parsing fails.
-// See: https://github.com/ethereum/solidity/issues/4871
-// solium-disable-next-line max-len
-import {BreakInvariantBounty, Target} from "../bounties/BreakInvariantBounty.sol";
-
-contract InsecureInvariantTargetMock is Target {
-  function checkInvariant() public returns(bool) {
-    return false;
-  }
-}
-
-contract InsecureInvariantTargetBounty is BreakInvariantBounty {
-  function _deployContract() internal returns (address) {
-    return new InsecureInvariantTargetMock();
-  }
-}