Tweak app.make_rattail_config() to allow caller to define some settings.

This is mostly for the sake of tests etc.

tests/data/tailbone.conf

@@ -0,0 +1,8 @@
+
+[app:main]
+edbob.config = %(here)s/tailbone.conf
+
+[rattail.db]
+keys = default, store
+default.url = sqlite://
+store.url = sqlite://

tests/test_app.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import unicode_literals
+
+import os
+from unittest import TestCase
+
+from sqlalchemy import create_engine
+
+from rattail.config import RattailConfig
+from rattail.exceptions import ConfigurationError
+from rattail.db import Session as RattailSession
+
+from tailbone import app
+from tailbone.db import Session as TailboneSession
+
+
+class TestRattailConfig(TestCase):
+
+    config_path = os.path.abspath(
+        os.path.join(os.path.dirname(__file__), 'data', 'tailbone.conf'))
+
+    def tearDown(self):
+        # may or may not be necessary depending on test
+        TailboneSession.remove()
+
+    def test_settings_arg_must_include_config_path_by_default(self):
+        # error raised if path not provided
+        self.assertRaises(ConfigurationError, app.make_rattail_config, {})
+        # get a config object if path provided
+        result = app.make_rattail_config({'edbob.config': self.config_path})
+        self.assertTrue(isinstance(result, RattailConfig))
+
+    def test_settings_arg_may_override_config_and_engines(self):
+        rattail_config = RattailConfig()
+        engine = create_engine('sqlite://')
+        result = app.make_rattail_config({
+            'rattail_config': rattail_config,
+            'rattail_engines': {'default': engine}})
+        self.assertTrue(result is rattail_config)
+        self.assertTrue(RattailSession.kw['bind'] is engine)
+        self.assertTrue(TailboneSession.bind is engine)