diff --git a/bigchaindb/models.py b/bigchaindb/models.py
index <HASH>..<HASH> 100644
--- a/bigchaindb/models.py
+++ b/bigchaindb/models.py
@@ -262,7 +262,7 @@ class Block(object):
             DoubleSpend: if the transaction is a double spend
             InvalidHash: if the hash of the transaction is wrong
             InvalidSignature: if the signature of the transaction is wrong
-            ValidationError: If the block contains a duplicated TX
+            DuplicateTransaction: If the block contains a duplicated TX
         """
         txids = [tx.id for tx in self.transactions]
         if len(txids) != len(set(txids)):
diff --git a/tests/pipelines/test_block_creation.py b/tests/pipelines/test_block_creation.py
index <HASH>..<HASH> 100644
--- a/tests/pipelines/test_block_creation.py
+++ b/tests/pipelines/test_block_creation.py
@@ -231,7 +231,7 @@ def test_full_pipeline(b, user_pk):
 def test_block_snowflake(create_tx, signed_transfer_tx):
     from bigchaindb.pipelines.block import tx_collector
     snowflake = tx_collector()
-    snowflake.send(create_tx)
+    assert snowflake.send(create_tx) == [create_tx]
     snowflake.send(signed_transfer_tx)
     snowflake.send(create_tx)
     assert snowflake.send(None) == [create_tx, signed_transfer_tx]
extra test for tx_collector and docs fix