diff --git a/tailbone/app.py b/tailbone/app.py
index 20ce4b80..28d64f00 100644
--- a/tailbone/app.py
+++ b/tailbone/app.py
@@ -55,22 +55,28 @@ def make_rattail_config(settings):
     """
     Make a Rattail config object from the given settings.
     """
-    # Initialize rattail config and embed it in the settings dict, to make it
-    # available to web requests later.
-    path = settings.get('edbob.config')
-    if not path or not os.path.exists(path):
-        raise ConfigurationError("Please set 'edbob.config' in [app:main] section of config "
-                                 "to the path of your config file.  Lame, but necessary.")
-    edbob.init('rattail', path)
-    log.info("using rattail config file: {0}".format(path))
-    rattail_config = RattailConfig(edbob.config)
-    settings['rattail_config'] = rattail_config
+    rattail_config = settings.get('rattail_config')
+    if not rattail_config:
 
-    # Load all Rattail database engines from config, and store in settings
-    # dict.  This is necessary e.g. in the case of a host server, to have
-    # access to its subordinate store servers.
-    rattail_engines = get_engines(rattail_config)
-    settings['rattail_engines'] = rattail_engines
+        # Initialize rattail config and embed it in the settings dict, to make it
+        # available to web requests later.
+        path = settings.get('edbob.config')
+        if not path or not os.path.exists(path):
+            raise ConfigurationError("Please set 'edbob.config' in [app:main] section of config "
+                                     "to the path of your config file.  Lame, but necessary.")
+        edbob.init('rattail', path)
+        log.info("using rattail config file: {0}".format(path))
+        rattail_config = RattailConfig(edbob.config)
+        settings['rattail_config'] = rattail_config
+
+    rattail_engines = settings.get('rattail_engines')
+    if not rattail_engines:
+
+        # Load all Rattail database engines from config, and store in settings
+        # dict.  This is necessary e.g. in the case of a host server, to have
+        # access to its subordinate store servers.
+        rattail_engines = get_engines(rattail_config)
+        settings['rattail_engines'] = rattail_engines
 
     # Configure the database session classes.  Note that most of the time we'll
     # be using the Tailbone Session, but occasionally (e.g. within batch
diff --git a/tests/data/tailbone.conf b/tests/data/tailbone.conf
new file mode 100644
index 00000000..4bdf2b74
--- /dev/null
+++ b/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://
diff --git a/tests/test_app.py b/tests/test_app.py
new file mode 100644
index 00000000..33962fd0
--- /dev/null
+++ b/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)