I have this code:
Token.sol
pragma solidity ^0.4.8;
contract Token {
    /* The amount of tokens a person will get for 1 ETH */
    uint256 public exchangeRate;
    /* The name of the token */
    string public name;
    /* The address which controls the token */
    address public owner;
    /* The symbol of the token */
    string public symbol;
    /* The balances of all registered addresses */
    mapping (address => uint256) balances;
    /* Token constructor */
    function Token(uint256 _exchangeRate, string _name, string _symbol) {
        exchangeRate = _exchangeRate;
        name = _name;
        owner = msg.sender;
        symbol = _symbol;
    }
    function getBalance(address account) returns (uint256 balance) {
        return balances[account];
    }
}
TestToken.sol
pragma solidity ^0.4.8;
// Framework libraries
import "truffle/Assert.sol";
import "truffle/DeployedAddresses.sol";
// Custom libraries and contracts
import "../contracts/Token.sol";
contract TestToken {
    function testExchangeRate() {
        Token token = new Token(500, "Dollar", "$");
        uint256 expected = 500;
        Assert.equal(token.exchangeRate(), expected, "The exchange rate should be 500 tokens for 1 ETH");
    }
    function testSymbol() {
        Token token = new Token(500, "Dollar", "$");
        Assert.equal(token.symbol(), "$", "The symbol of the token should be $");
    }
}
And I get this error when I try to execute it:
Error: Member "equal" is not available in type(library Assert) outside of storage.
        Assert.equal(token.symbol(), "$", "The symbol of the token should be $");
        ^----------^
Compiliation failed. See above.