Problem: No tests for invalid proposer or multiple inputs

Solution: Add tests which raise InvalidPropser exception if the public key not a
part of the validator set and raises MultipleInputsError if more than 1
validators `owners_before` in the election.

bigchaindb/upsert_validator/validator_election.py

@@ -73,6 +73,8 @@ class ValidatorElection(Transaction):
 
     def validate(self, bigchain, current_transactions=[]):
         """Validate election transaction
+        For more details refer BEP-21: https://github.com/bigchaindb/BEPs/tree/master/21
+
         NOTE:
         * A valid election is initiated by an existing validator.
 
@@ -80,15 +82,13 @@ class ValidatorElection(Transaction):
           alloacted according to the voting power of each validator node.
 
         Args:
-            bigchain (BigchainDB): an instantiated bigchaindb.tendermint.BigchainDB object.
+            bigchain (BigchainDB): an instantiated bigchaindb.lib.BigchainDB object.
 
         Returns:
-            The transaction (Transaction) if the transaction is valid else it
-            raises an exception describing the reason why the transaction is
-            invalid.
+            `True` if the election is valid
 
         Raises:
-            ValidationError: If the transaction is invalid
+            ValidationError: If the election is invalid
         """
         input_conditions = []
 
@@ -103,7 +103,7 @@ class ValidatorElection(Transaction):
         current_validators = self.current_validators(bigchain)
 
         # NOTE: Proposer should be a single node
-        if len(self.inputs) != 1:
+        if len(self.inputs) != 1 or len(self.inputs[0].owners_before) != 1:
             raise MultipleInputsError('`tx_signers` must be a list instance of length one')
 
         # NOTE: change more than 1/3 of the current power is not allowed

tests/upsert_validator/test_validator_election.py

@@ -3,6 +3,8 @@ import pytest
 from bigchaindb.upsert_validator import ValidatorElection
 from bigchaindb.common.exceptions import (DuplicateTransaction,
                                           UnequalValidatorSet,
+                                          InvalidProposer,
+                                          MultipleInputsError,
                                           InvalidPowerChange)
 
 pytestmark = [pytest.mark.tendermint, pytest.mark.bdb]
@@ -27,6 +29,30 @@ def test_upsert_validator_invalid_power_election(b_mock, new_validator, node_key
         election.validate(b_mock)
 
 
+def test_upsert_validator_invalid_proposed_election(b_mock, new_validator, node_key):
+    from bigchaindb.common.crypto import generate_key_pair
+
+    alice = generate_key_pair()
+    voters = ValidatorElection.recipients(b_mock)
+    election = ValidatorElection.generate([alice.public_key],
+                                          voters,
+                                          new_validator, None).sign([alice.private_key])
+    with pytest.raises(InvalidProposer):
+        election.validate(b_mock)
+
+
+def test_upsert_validator_invalid_inputs_election(b_mock, new_validator, node_key):
+    from bigchaindb.common.crypto import generate_key_pair
+
+    alice = generate_key_pair()
+    voters = ValidatorElection.recipients(b_mock)
+    election = ValidatorElection.generate([node_key.public_key, alice.public_key],
+                                          voters,
+                                          new_validator, None).sign([node_key.private_key, alice.private_key])
+    with pytest.raises(MultipleInputsError):
+        election.validate(b_mock)
+
+
 def test_upsert_validator_invalid_election(b_mock, new_validator, node_key):
     voters = ValidatorElection.recipients(b_mock)
     valid_election = ValidatorElection.generate([node_key.public_key],