Add error handling

bigchaindb/backend/connection.py

@@ -1,11 +1,24 @@
-class ConnectionError(Exception):
-    """Raised when there is a connection error when running a query."""
+from bigchaindb.common.exceptions import ConfigurationError
+from importlib import import_module
+
+
+BACKENDS = {
+    'rethinkdb': 'bigchaindb.backend.rethinkdb.connection.RethinkDBConnection'
+}
+
+
+def connect(backend, host, port, dbname):
+    try:
+        module_name, _, class_name = BACKENDS[backend].rpartition('.')
+        Class = getattr(import_module(module_name), class_name)
+    except KeyError:
+        raise ConfigurationError('Backend `{}` is not supported. '
+                                 'BigchainDB currently supports {}'.format(backend, BACKENDS.keys()))
+    except (ImportError, AttributeError) as exc:
+        raise ConfigurationError('Error loading backend `{}`'.format(backend)) from exc
+
+    return Class(host, port, dbname)
 
 
 class Connection:
-
-    def run(self):
-        raise NotImplementedError()
-
-    def connect(self):
-        raise NotImplementedError()
+    pass

tests/backend/test_connection.py

@@ -1,3 +1,6 @@
+import pytest
+
+
 def test_get_connection_returns_the_correct_instance():
     from bigchaindb.backend import connect
     from bigchaindb.backend.connection import Connection
@@ -13,3 +16,18 @@ def test_get_connection_returns_the_correct_instance():
     conn = connect(**config)
     assert isinstance(conn, Connection)
     assert isinstance(conn, RethinkDBConnection)
+
+
+def test_get_connection_raises_a_configuration_error(monkeypatch):
+    from bigchaindb.common.exceptions import ConfigurationError
+    from bigchaindb.backend import connect
+
+    with pytest.raises(ConfigurationError):
+        connect('msaccess', 'localhost', '1337', 'mydb')
+
+    with pytest.raises(ConfigurationError):
+        # We need to force a misconfiguration here
+        monkeypatch.setattr('bigchaindb.backend.connection.BACKENDS',
+                            {'catsandra': 'bigchaindb.backend.meowmeow.Catsandra'})
+
+        connect('catsandra', 'localhost', '1337', 'mydb')