fix a problem when revoke is called twice

contracts/token/TokenVesting.sol

@@ -27,6 +27,7 @@ contract TokenVesting is Ownable {
   bool revocable;
 
   mapping (address => uint256) released;
+  mapping (address => bool) revoked;
 
   /**
    * @dev Creates a vesting contract that vests its balance of any ERC20 token to the
@@ -65,17 +66,22 @@ contract TokenVesting is Ownable {
   }
 
   /**
-   * @notice Allows the owner to revoke the vesting. Tokens already vested remain in the contract.
+   * @notice Allows the owner to revoke the vesting. Tokens already vested
+   * remain in the contract, the rest are returned to the owner.
    * @param token ERC20 token which is being vested
    */
   function revoke(ERC20Basic token) onlyOwner {
     require(revocable);
+    require(!revoked[token]);
 
     uint256 balance = token.balanceOf(this);
 
     uint256 vested = vestedAmount(token);
+    uint256 vesting = balance - vested;
 
-    token.transfer(owner, balance - vested);
+    revoked[token] = true;
+
+    token.transfer(owner, vesting);
 
     Revoked();
   }
@@ -87,7 +93,7 @@ contract TokenVesting is Ownable {
   function vestedAmount(ERC20Basic token) constant returns (uint256) {
     if (now < cliff) {
       return 0;
-    } else if (now >= start + duration) {
+    } else if (now >= start + duration || revoked[token]) {
       return token.balanceOf(this);
     } else {
       uint256 currentBalance = token.balanceOf(this);

test/TokenVesting.js

@@ -80,8 +80,7 @@ contract('TokenVesting', function ([_, owner, beneficiary]) {
   });
 
   it('should return the non-vested tokens when revoked by owner', async function () {
-    await increaseTimeTo(this.start + this.cliff + duration.weeks(1));
-    await this.vesting.release(this.token.address);
+    await increaseTimeTo(this.start + this.cliff + duration.weeks(12));
 
     const vested = await this.vesting.vestedAmount(this.token.address);
     const balance = await this.token.balanceOf(this.vesting.address);
@@ -93,15 +92,25 @@ contract('TokenVesting', function ([_, owner, beneficiary]) {
   });
 
   it('should keep the vested tokens when revoked by owner', async function () {
-    await increaseTimeTo(this.start + this.cliff + duration.weeks(1));
-    await this.vesting.release(this.token.address);
+    await increaseTimeTo(this.start + this.cliff + duration.weeks(12));
+
+    const vestedPre = await this.vesting.vestedAmount(this.token.address);
+
+    await this.vesting.revoke(this.token.address, { from: owner });
+
+    const vestedPost = await this.vesting.vestedAmount(this.token.address);
+
+    vestedPre.should.bignumber.equal(vestedPost);
+  });
+
+  it('should fail to be revoked a second time', async function () {
+    await increaseTimeTo(this.start + this.cliff + duration.weeks(12));
 
     const vested = await this.vesting.vestedAmount(this.token.address);
 
     await this.vesting.revoke(this.token.address, { from: owner });
 
-    const balance = await this.token.balanceOf(this.vesting.address);
-    balance.should.bignumber.equal(vested);
+    await this.vesting.revoke(this.token.address, { from: owner }).should.be.rejectedWith(EVMThrow);
   });
 
 });