Test consensus (#398)

* Remove unused import

* Simplify and group the imports

* Add extra space (pep 8)

* Remove NotImplementedError

the class BaseConsensusRules implements verify_vote_signature

* Add test module for consensus module

bigchaindb/consensus.py

@@ -1,9 +1,6 @@
-import copy
 from abc import ABCMeta, abstractmethod
 
-import bigchaindb.exceptions as exceptions
+from bigchaindb import crypto, exceptions, util
-from bigchaindb import util
-from bigchaindb import crypto
 
 
 class AbstractConsensusRules(metaclass=ABCMeta):
@@ -101,7 +98,7 @@ class AbstractConsensusRules(metaclass=ABCMeta):
             bool: True if the votes's required signature data is present
                 and correct, False otherwise.
         """
-        raise NotImplementedError
+
 
 class BaseConsensusRules(AbstractConsensusRules):
     """Base consensus rules for Bigchain.

tests/test_consensus.py

@@ -0,0 +1,15 @@
+import pytest
+
+
+class TestBaseConsensusRules(object):
+
+    def test_validate_transaction(self):
+        from bigchaindb.consensus import BaseConsensusRules
+        transaction = {
+            'transaction': {
+                'operation': None,
+                'fulfillments': None,
+            },
+        }
+        with pytest.raises(ValueError):
+            BaseConsensusRules.validate_transaction(None, transaction)