Problem: Inconsitant error handling

Solution: All errors should generate exceptions extended from ValidationError class

bigchaindb/common/exceptions.py

@@ -106,3 +106,15 @@ class MultipleValidatorOperationError(ValidationError):
 
 class MultipleInputsError(ValidationError):
     """Raised if there were multiple inputs when only one was expected"""
+
+
+class InvalidProposer(ValidationError):
+    """Raised if the public key is not a part of the validator set"""
+
+
+class UnequalValidatorSet(ValidationError):
+    """Raised if the validator sets differ"""
+
+
+class InvalidPowerChange(ValidationError):
+    """Raised if proposed power change in validator set is >=1/3 total power"""

bigchaindb/upsert_validator/validator_election.py

@@ -1,4 +1,8 @@
-from bigchaindb.common.exceptions import (InvalidSignature, MultipleInputsError,
+from bigchaindb.common.exceptions import (InvalidSignature,
+                                          MultipleInputsError,
+                                          InvalidProposer,
+                                          UnequalValidatorSet,
+                                          InvalidPowerChange,
                                           DuplicateTransaction)
 from bigchaindb.tendermint_utils import key_from_base64
 from bigchaindb.common.crypto import (public_key_from_ed25519_key)
@@ -104,15 +108,18 @@ class ValidatorElection(Transaction):
 
         # NOTE: change more than 1/3 of the current power is not allowed
         if self.asset['data']['power'] >= (1/3)*sum(current_validators.values()):
-            raise ValueError('`power` must be less than 1/3 of total power')
+            raise InvalidPowerChange('`power` change must be less than 1/3 of total power')
 
         # NOTE: Check if the proposer is a validator.
         [election_initiator_node_pub_key] = self.inputs[0].owners_before
         if election_initiator_node_pub_key not in current_validators.keys():
-            return False
+            raise InvalidProposer('Public key is not a part of the validator set')
 
         # NOTE: Check if all validators have been assigned votes equal to their voting power
-        return self.is_same_topology(current_validators, self.outputs)
+        if not self.is_same_topology(current_validators, self.outputs):
+            raise UnequalValidatorSet('Validator set much be exactly same to the outputs of election')
+
+        return True
 
     @classmethod
     def generate(cls, initiator, voters, election_data, metadata=None):

tests/upsert_validator/test_validator_election.py

@@ -1,7 +1,9 @@
 import pytest
 
 from bigchaindb.upsert_validator import ValidatorElection
-from bigchaindb.common.exceptions import DuplicateTransaction
+from bigchaindb.common.exceptions import (DuplicateTransaction,
+                                          UnequalValidatorSet,
+                                          InvalidPowerChange)
 
 pytestmark = [pytest.mark.tendermint, pytest.mark.bdb]
 
@@ -21,7 +23,7 @@ def test_upsert_validator_invalid_power_election(b_mock, new_validator, node_key
     election = ValidatorElection.generate([node_key.public_key],
                                           voters,
                                           new_validator, None).sign([node_key.private_key])
-    with pytest.raises(ValueError):
+    with pytest.raises(InvalidPowerChange):
         election.validate(b_mock)
 
 
@@ -46,7 +48,9 @@ def test_upsert_validator_invalid_election(b_mock, new_validator, node_key):
     invalid_election = ValidatorElection.generate([node_key.public_key],
                                                   voters[1:],
                                                   new_validator, None).sign([node_key.private_key])
-    assert not invalid_election.validate(b_mock)
+
+    with pytest.raises(UnequalValidatorSet):
+        invalid_election.validate(b_mock)
 
     recipients = ValidatorElection.recipients(b_mock)
     altered_recipients = []
@@ -59,4 +63,5 @@ def test_upsert_validator_invalid_election(b_mock, new_validator, node_key):
                                              altered_recipients,
                                              new_validator, None).sign([node_key.private_key])
 
-    assert not tx_election.validate(b_mock)
+    with pytest.raises(UnequalValidatorSet):
+        tx_election.validate(b_mock)