Merge pull request #341 from lsaether/master

Added contracts/token/BurnableToken.sol

contracts/token/BurnableToken.sol

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+pragma solidity ^0.4.13;
+
+import './StandardToken.sol';
+
+/**
+ * @title Burnable Token
+ * @dev Token that can be irreversibly burned (destroyed).
+ */
+contract BurnableToken is StandardToken {
+
+    /**
+     * @dev Burns a specific amount of tokens.
+     * @param _value The amount of token to be burned.
+     */
+    function burn(uint _value)
+        public
+    {
+        require(_value > 0);
+
+        address burner = msg.sender;
+        balances[burner] = balances[burner].sub(_value);
+        totalSupply = totalSupply.sub(_value);
+        Burn(burner, _value);
+    }
+
+    event Burn(address indexed burner, uint indexed value);
+}

test/BurnableToken.js

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+'use strict'
+
+const EVMThrow = require('./helpers/EVMThrow.js')
+const BurnableTokenMock = artifacts.require("./helpers/BurnableTokenMock.sol")
+const BigNumber = web3.BigNumber
+
+require('chai')
+  .use(require('chai-as-promised'))
+  .use(require('chai-bignumber')(BigNumber))
+  .should()
+
+const expect = require('chai').expect
+
+contract('BurnableToken', function (accounts) {
+    let token 
+    let expectedTokenSupply = new BigNumber(999)
+
+    beforeEach(async function () {
+        token = await BurnableTokenMock.new(accounts[0], 1000)
+    })
+
+    it('owner should be able to burn tokens', async function () {
+        const { logs } = await token.burn(1, { from: accounts[0] })
+
+        const balance = await token.balanceOf(accounts[0])
+        balance.should.be.bignumber.equal(expectedTokenSupply)
+
+        const totalSupply = await token.totalSupply()
+        totalSupply.should.be.bignumber.equal(expectedTokenSupply)
+
+        const event = logs.find(e => e.event === 'Burn')
+        expect(event).to.exist
+    })
+
+    it('cannot burn more tokens than your balance', async function () {
+        await token.burn(2000, { from: accounts[0] })
+        .should.be.rejectedWith(EVMThrow) 
+    })
+})

test/helpers/BurnableTokenMock.sol

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+pragma solidity ^0.4.13;
+
+import '../../contracts/token/BurnableToken.sol';
+
+contract BurnableTokenMock is BurnableToken {
+
+  function BurnableTokenMock(address initialAccount, uint initialBalance) {
+    balances[initialAccount] = initialBalance;
+    totalSupply = initialBalance;
+  }
+
+}