Retrieve default backend from env if set.

Fixed tests.

bigchaindb/__init__.py

@@ -20,6 +20,11 @@ _database_mongodb = {
     'replicaset': os.environ.get('BIGCHAINDB_DATABASE_REPLICASET', 'bigchain-rs'),
 }
 
+_database_map = {
+    'mongodb': _database_mongodb,
+    'rethinkdb': _database_rethinkdb
+}
+
 config = {
     'server': {
         # Note: this section supports all the Gunicorn settings:
@@ -28,7 +33,9 @@ config = {
         'workers': None,  # if none, the value will be cpu_count * 2 + 1
         'threads': None,  # if none, the value will be cpu_count * 2 + 1
     },
-    'database': _database_rethinkdb,
+    'database': _database_map[
+        os.environ.get('BIGCHAINDB_DATABASE_BACKEND', 'rethinkdb')
+    ],
     'keypair': {
         'public': None,
         'private': None,

tests/test_config_utils.py

@@ -131,6 +131,27 @@ def test_autoconfigure_read_both_from_file_and_env(monkeypatch, request):
     from bigchaindb import config_utils
     config_utils.autoconfigure()
 
+    backend = request.config.getoption('--database-backend')
+    database_rethinkdb = {
+        'backend': 'rethinkdb',
+        'host': 'test-host',
+        'port': 4242,
+        'name': 'test-dbname',
+    }
+    database_mongodb = {
+        'backend': 'mongodb',
+        'host': 'test-host',
+        'port': 4242,
+        'name': 'test-dbname',
+        'replicaset': 'bigchain-rs',
+    }
+
+    database = {}
+    if backend == 'mongodb':
+        database = database_mongodb
+    elif backend == 'rethinkdb':
+        database = database_rethinkdb
+
     assert bigchaindb.config == {
         'CONFIGURED': True,
         'server': {
@@ -138,12 +159,7 @@ def test_autoconfigure_read_both_from_file_and_env(monkeypatch, request):
             'workers': None,
             'threads': None,
         },
-        'database': {
+        'database': database,
-            'backend': request.config.getoption('--database-backend'),
-            'host': 'test-host',
-            'port': 4242,
-            'name': 'test-dbname',
-        },
         'keypair': {
             'public': None,
             'private': None,