[Workaround]: Travis failures

- Marking test_double_create as serial
- If this works, we don't need to skip the tests
- Finger crossed.

.ci/travis_script.sh

@@ -7,11 +7,14 @@ if [[ -n ${TOXENV} ]]; then
 elif [[ "${BIGCHAINDB_DATABASE_BACKEND}" == mongodb && \
     -z "${BIGCHAINDB_DATABASE_SSL}" ]]; then
     # Run the full suite of tests for MongoDB over an unsecure connection
-  pytest -sv --database-backend=mongodb --cov=bigchaindb
+  pytest -sv --database-backend=mongodb -m "serial"
+  pytest -sv --database-backend=mongodb --cov=bigchaindb -m "not serial"
 elif [[ "${BIGCHAINDB_DATABASE_BACKEND}" == mongodb && \
     "${BIGCHAINDB_DATABASE_SSL}" == true ]]; then
     # Run a sub-set of tests over SSL; those marked as 'pytest.mark.bdb_ssl'.
   pytest -sv --database-backend=mongodb-ssl --cov=bigchaindb -m bdb_ssl
 else
-  pytest -sv -n auto --cov=bigchaindb
+  # Run the full suite of tests for RethinkDB (the default backend when testing)
+  pytest -sv -m "serial"
+  pytest -sv --cov=bigchaindb -m "not serial"
 fi

tests/integration/test_federation.py

@@ -116,8 +116,8 @@ def test_elect_valid(federation_3):
 
 
 @pytest.mark.bdb
-@pytest.mark.skip_travis_rdb
 @pytest.mark.genesis
+@pytest.mark.skip_travis_rdb
 def test_elect_invalid(federation_3):
     [bx, (s0, s1, s2)] = federation_3
     tx = input_single_create(bx[0])

tests/integration/test_integration.py

@@ -5,7 +5,7 @@ import pytest
 pytestmark = [pytest.mark.bdb, pytest.mark.usefixtures('processes')]
 
 
-@pytest.mark.skip_travis_rdb
+@pytest.mark.serial
 def test_double_create(b, user_pk):
     from bigchaindb.models import Transaction
     from bigchaindb.backend.query import count_blocks