[Ethereum] truffle always says “.the_function is not a function”

If you are running the latest version of Truffle (v.3.x), the way to call a function or variable in your contract has evolved a little bit according to the Upgrading documentation

In Truffle 2.0, your contract abstractions managed your networks in a naive way, and added constructs like a "default network" that opened up the possibility of using the wrong network artifacts and deployed addresses at the wrong time. This provided a fancy and easy to use syntax – i.e., MyContract.deployed().myFunction(...) – but it left your code open to errors. Truffle 3.0 changes this syntax, where .deployed() is now thennable, like a promise (see example below). Similarly, this makes your contract abstractions seamlessly integrate with EIP 190, Ethereum's package management standard. All of this is for the better, but it means you'll have some changes to make all across the board.

So in your case, if you want to call a function, you have to do this:

HelloWorld.deployed().then(function(instance) {
    return instance.balance.call();
}).then(function(balance) {
    console.log(balance);
});

Please refer to the latest documentation for more details.

Assuming your successfully deployed the contract with $ truffle migrate --reset ... Need to reset every time you start testrpc.

I think the problem is it's asynchronous and you're not waiting for Congress.deployed(); to finish.

I'm not up to full speed in 3.x due to the breaking changes, but based on what I've read in http://truffleframework.com/tutorials/upgrading-from-truffle-2-to-3#contract-abstractions-deployed-is-now-thennable, deployed is now thennable, so something like ...

var congress;    
contract('Congress', function(accounts) {
  it("adding new member", function() {
    Congress.deployed() // wait for the response
    .then(function(temp) {
      congress = temp;
      return congress.addMember("John", 100, 100, 50, "buyer", {from:accounts[1]});
    })
    .then(function(txn){
      console.log(txn);
      // carry on
    });
  });
});

Hope it helps.