diff --git a/bigchaindb/common/memoize.py b/bigchaindb/common/memoize.py
index f52c1dc3..9342ea84 100644
--- a/bigchaindb/common/memoize.py
+++ b/bigchaindb/common/memoize.py
@@ -5,7 +5,7 @@ from functools import lru_cache
 
 class HDict(dict):
     def __hash__(self):
-        return  int.from_bytes(codecs.decode(self['id'], 'hex'), 'big')
+        return hash(codecs.decode(self['id'], 'hex'))
 
 
 @lru_cache(maxsize=16384)
@@ -17,9 +17,9 @@ def memoize_from_dict(func):
 
     @functools.wraps(func)
     def memoized_func(*args, **kwargs):
-        print(args)
-        new_args = (args[0], HDict(args[1]), args[2])
-        print(new_args)
+        args = list(args)
+        args[1] = HDict(args[1])
+        new_args = tuple(args)
         return from_dict(func, *new_args, **kwargs)
 
     return memoized_func
diff --git a/bigchaindb/lib.py b/bigchaindb/lib.py
index e00e75f5..4c45beda 100644
--- a/bigchaindb/lib.py
+++ b/bigchaindb/lib.py
@@ -77,10 +77,11 @@ class BigchainDB(object):
             raise ValidationError('Mode must be one of the following {}.'
                                   .format(', '.join(self.mode_list)))
 
+        tx_dict = transaction.tx_dict if transaction.tx_dict else transaction.to_dict()
         payload = {
             'method': mode,
             'jsonrpc': '2.0',
-            'params': [encode_transaction(transaction.to_dict())],
+            'params': [encode_transaction(tx_dict)],
             'id': str(uuid4())
         }
         # TODO: handle connection errors!
diff --git a/tests/conftest.py b/tests/conftest.py
index 0fd4d671..cc985d96 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -256,7 +256,8 @@ def b():
 def create_tx(alice, user_pk):
     from bigchaindb.models import Transaction
     name = f'I am created by the create_tx fixture. My random identifier is {random.random()}.'
-    return Transaction.create([alice.public_key], [([user_pk], 1)], asset={'name': name})
+    return Transaction.create([alice.public_key], [([user_pk], 1)], asset={'name': name})\
+                      .sign([alice.private_key])
 
 
 @pytest.fixture