add stepDefend success testcase (ethereum-optimism#11148)

packages/contracts-bedrock/test/dispute/FaultDisputeGame.t.sol

@@ -846,6 +846,39 @@ contract FaultDisputeGame_Test is FaultDisputeGame_Init {
         gameProxy.step(8, true, claimData5, hex"");
     }
 
+    /// @dev Tests that successfully step with true defend claim when there is a true defend claim(claim7) in the
+    /// middle of the dispute game.
+    function test_stepDefendDummyClaim_defendTrueClaimInTheMiddle_succeeds() public {
+        // Give the test contract some ether
+        vm.deal(address(this), 1000 ether);
+
+        // Make claims all the way down the tree.
+        (,,,, Claim disputed,,) = gameProxy.claimData(0);
+        gameProxy.attack{ value: _getRequiredBond(0) }(disputed, 0, _dummyClaim());
+        (,,,, disputed,,) = gameProxy.claimData(1);
+        gameProxy.attack{ value: _getRequiredBond(1) }(disputed, 1, _dummyClaim());
+        (,,,, disputed,,) = gameProxy.claimData(2);
+        gameProxy.attack{ value: _getRequiredBond(2) }(disputed, 2, _dummyClaim());
+        (,,,, disputed,,) = gameProxy.claimData(3);
+        gameProxy.attack{ value: _getRequiredBond(3) }(disputed, 3, _dummyClaim());
+        (,,,, disputed,,) = gameProxy.claimData(4);
+        gameProxy.attack{ value: _getRequiredBond(4) }(disputed, 4, _changeClaimStatus(_dummyClaim(), VMStatuses.PANIC));
+
+        bytes memory claimData7 = abi.encode(7, 7);
+        Claim postState_ = Claim.wrap(gameImpl.vm().step(claimData7, hex"", bytes32(0)));
+
+        (,,,, disputed,,) = gameProxy.claimData(5);
+        gameProxy.attack{ value: _getRequiredBond(5) }(disputed, 5, _dummyClaim());
+        (,,,, disputed,,) = gameProxy.claimData(6);
+        bytes memory _dummyClaimData = abi.encode(gasleft(), gasleft());
+        gameProxy.defend{ value: _getRequiredBond(6) }(disputed, 6, postState_);
+        (,,,, disputed,,) = gameProxy.claimData(7);
+
+        gameProxy.attack{ value: _getRequiredBond(7) }(disputed, 7, Claim.wrap(keccak256(claimData7)));
+        gameProxy.addLocalData(LocalPreimageKey.DISPUTED_L2_BLOCK_NUMBER, 8, 0);
+        gameProxy.step(8, false, claimData7, hex"");
+    }
+
     /// @dev Tests that step reverts with false attacking claim when there is a true defend claim(claim5) in the middle
     /// of the dispute game.
     function test_stepAttackTrueClaim_defendTrueClaimInTheMiddle_reverts() public {