Probando contratos con trufa

Estoy tratando de escribir pruebas para contratos usando trufa; He abierto un tema aquí . El flujo de trabajo es el siguiente:

mkdir truffle_testing
truffle init
rm -r tests/* contracts/* build/*

A continuación, creo los siguientes archivos de contrato en el directorio contracts/ :

C.sol

contract C {

    string words = "Bla bla bla";

    uint256 lastVal;

    function math(uint256 a, uint256 b) {
        lastVal = a + b;
    }

    function getVal() constant returns (uint256) {
    return lastVal;
    }

    function getWords() constant returns (string) {
        return words;
    }
}

y

Migraciones.sol

contract Migrations {
  address public owner;

  // A function with the signature `last_completed_migration()`, returning a uint, is required.
  uint public last_completed_migration;

  modifier restricted() {
    if (msg.sender == owner) _
  }

  function Migrations() {
    owner = msg.sender;
  }

  // A function with the signature `setCompleted(uint)` is required.
  function setCompleted(uint completed) restricted {
    last_completed_migration = completed;
  }

  function upgrade(address new_address) restricted {
    Migrations upgraded = Migrations(new_address);
    upgraded.setCompleted(last_completed_migration);
  }
}

Luego creo un conjunto de pruebas en el directorio tests/ :

contract('C', function(accounts) {
  it("Getting the words string from the contract", function() {
    var c = C.deployed();

    return c.getWords.call(accounts[0]).then(function(words) {
      assert.equal(words, "Bla bla bla", "[E] The contract should have said \"Bla bla bla\"");
    });
  });

  it(" 2 + 2 = 4 ", function(){
    var c = C.deployed();
    // Call method to initialize value (this method only returns the tx id and not the
    // actual value)
    c.math(2, 2, {from:accounts[0],gas:3000000}).then(function(tx_that_we_dont_need) {    
        return c.getVal.call().then(function(additionResult){
            assert.equal(additionResult, 4, "[E] 2 + 2 = 4 even in eth. contracts.");
       });
    });
  });
});

Después de escribir todos los archivos, lanzo testrpc :

testrpc:

EthereumJS TestRPC v2.1.0

Available Accounts
==================
...

luego construye el proyecto:

truffle compile --compile-all
truffle migrate
truffle test

Como era de esperar, todas las pruebas pasan pero también pasan si cambio el valor en la segunda prueba de 4 a cualquier otro valor entero.

¿Por qué?

Editar:

Agregué la devolución de llamada realizada a mis pruebas, pero no funciona (las pruebas aún se muestran como aprobadas cuando no deberían):

contract('C', function(accounts) {
  it("Getting the words string from the contract", function() {
    var c = C.deployed();

    return c.getWords.call(accounts[0]).then(function(words) {
      assert.equal(words, "Bla bla bla", "[E] The contract should have said \"Bla bla bla\"");
    });
  });

  it(" 2 + 2 = 4 ", function(){
    var c = C.deployed();
    // Call method to initialize value (this method only returns the tx id and not the
    // actual value)
    c.math(2, 2, {from:accounts[0],gas:3000000}).then(function() {    
        return c.getVal.call().then(function(additionResult){
            assert.equal(additionResult, 6, "[E] 2 + 2 = 4 even in eth. contracts.");
        done();
       }).done(null, function(error) {
        done(error); 
       });
    });
  });

});

Editar #2:

He intentado ejecutar el siguiente código:

contract('C', function(accounts) {
  it("Getting the words string from the contract", function() {
    var c = C.deployed();

    return c.getWords.call(accounts[0]).then(function(words) {
      assert.equal(words, "Bla bla bla", "[E] The contract should have said \"Bla bla bla\"");
    });
  });

  it(" 2 + 2 = 4 ", function(){
    var c = C.deployed();
    // Call method to initialize value (this method only returns the tx id and not the
    // actual value)
    c.math(2, 2, {from:accounts[0],gas:3000000}).then(function() {    
        return c.getVal.call().then(function(additionResult){
            assert.equal(additionResult, 6, "[E] 2 + 2 = 4 even in eth. contracts.");
        done();
       }).done(null, function(error) {
        done(error); 
       });
    });
  });

});

pero ahora aparece un error de tiempo de espera:

Contract: C
    ✓ Getting the words string from the contract (232ms)


    1)  2 + 2 = 4 
    > No events were emitted


  1 passing (5m)
  1 failing

  1) Contract: C  2 + 2 = 4 :
     Error: timeout of 300000ms exceeded. Ensure the done() callback is being called in this test.