core: implemented a queued approach processing transactions

Implemented a new transaction queue. Transactions with a holes in their
nonce sequence are also not propagated over the network.

N: 0,1,2,5,6,7 = propagate 0..2 -- 5..N is kept in the tx pool

core/transaction_pool_test.go

@@ -56,7 +56,57 @@ func TestInvalidTransactions(t *testing.T) {
 	tx.SignECDSA(key)
 
 	err = pool.Add(tx)
-	if err != ErrImpossibleNonce {
-		t.Error("expected", ErrImpossibleNonce)
+	if err != ErrNonce {
+		t.Error("expected", ErrNonce)
+	}
+}
+
+func TestTransactionQueue(t *testing.T) {
+	pool, key := setupTxPool()
+	tx := transaction()
+	tx.SignECDSA(key)
+	from, _ := tx.From()
+	pool.currentState().AddBalance(from, big.NewInt(1))
+	pool.addTx(tx)
+
+	pool.checkQueue()
+	if len(pool.txs) != 1 {
+		t.Error("expected valid txs to be 1 is", len(pool.txs))
+	}
+
+	tx = transaction()
+	tx.SignECDSA(key)
+	from, _ = tx.From()
+	pool.currentState().SetNonce(from, 10)
+	tx.SetNonce(1)
+	pool.addTx(tx)
+	pool.checkQueue()
+	if _, ok := pool.txs[tx.Hash()]; ok {
+		t.Error("expected transaction to be in tx pool")
+	}
+
+	if len(pool.queue[from]) != 0 {
+		t.Error("expected transaction queue to be empty. is", len(pool.queue[from]))
+	}
+
+	pool, key = setupTxPool()
+	tx1, tx2, tx3 := transaction(), transaction(), transaction()
+	tx2.SetNonce(10)
+	tx3.SetNonce(11)
+	tx1.SignECDSA(key)
+	tx2.SignECDSA(key)
+	tx3.SignECDSA(key)
+	pool.addTx(tx1)
+	pool.addTx(tx2)
+	pool.addTx(tx3)
+	from, _ = tx1.From()
+	pool.checkQueue()
+
+	if len(pool.txs) != 1 {
+		t.Error("expected tx pool to be 1 =")
+	}
+
+	if len(pool.queue[from]) != 2 {
+		t.Error("expected transaction queue to be empty. is", len(pool.queue[from]))
 	}
 }