Add memory backend (#394)

* Add simple backend

* Add test case for simple backend

* Add tests for mget backend method

* Fix redis mock mget implementation

* Make sure memory backend is thread safe

* Add docs section for memory backend

* Add test usage examples to docs

* Update docs for memory backend in testing

* Share memory storage between threads

constance/backends/memory.py

@@ -0,0 +1,38 @@
+from threading import Lock
+
+from . import Backend
+from .. import signals, config
+
+
+class MemoryBackend(Backend):
+    """
+    Simple in-memory backend that should be mostly used for testing purposes
+    """
+    _storage = {}
+    _lock = Lock()
+
+    def __init__(self):
+        super().__init__()
+
+    def get(self, key):
+        with self._lock:
+            return self._storage.get(key)
+
+    def mget(self, keys):
+        if not keys:
+            return
+        result = []
+        with self._lock:
+            for key in keys:
+                value = self._storage.get(key)
+                if value is not None:
+                    result.append((key, value))
+        return result
+
+    def set(self, key, value):
+        with self._lock:
+            old_value = self._storage.get(key)
+            self._storage[key] = value
+            signals.config_updated.send(
+                sender=config, key=key, old_value=old_value, new_value=value
+            )

docs/backends.rst

@@ -144,3 +144,15 @@ configured cache backend to enable this feature, e.g. "default"::
           setting to ``None``.
 
 .. _django-picklefield: http://pypi.python.org/pypi/django-picklefield/
+
+Memory
+------
+
+The configuration values are stored in a memory and do not persist between process
+restarts. In order to use this backend you must set the ``CONSTANCE_BACKEND``
+Django setting to::
+
+    CONSTANCE_BACKEND = 'constance.backends.memory.MemoryBackend'
+
+The main purpose of this one is to be used mostly for testing/developing means,
+so make sure you intentionally use it on production environments.

docs/testing.rst

@@ -41,7 +41,7 @@ method level and also as a
 
 
 Pytest usage
-~~~~~
+~~~~~~~~~~~~
 
 Django-constance provides pytest plugin that adds marker
 :class:`@pytest.mark.override_config()`. It handles config override for
@@ -108,3 +108,16 @@ Any scope, auto-used fixture alternative can also be implemented like this
         with override_config(API_URL="/awesome/url/"):
             yield
 
+
+Memory backend
+~~~~~~~~~~~~~~
+
+If you don't want to rely on any external services such as Redis or database when
+running your unittests you can select :class:`MemoryBackend` for a test Django settings file
+
+.. code-block:: python
+
+    CONSTANCE_BACKEND = 'constance.backends.memory.MemoryBackend'
+
+It will provide simple thread-safe backend which will reset to default values after each
+test run.

tests/backends/test_memory.py

@@ -0,0 +1,18 @@
+from django.test import TestCase
+
+from constance import settings
+
+from tests.storage import StorageTestsMixin
+
+
+class TestMemory(StorageTestsMixin, TestCase):
+
+    def setUp(self):
+        self.old_backend = settings.BACKEND
+        settings.BACKEND = 'constance.backends.memory.MemoryBackend'
+        super().setUp()
+        self.config._backend._storage = {}
+
+    def tearDown(self):
+        self.config._backend._storage = {}
+        settings.BACKEND = self.old_backend

tests/redis_mockup.py

@@ -3,9 +3,4 @@ class Connection(dict):
         self[key] = value
 
     def mget(self, keys):
-        values = []
-        for key in keys:
-            value = self.get(key, None)
-            if value is not None:
-                values.append(value)
-        return values
+        return [self.get(key) for key in keys]

tests/storage.py

@@ -1,6 +1,7 @@
 from datetime import datetime, date, time, timedelta
 from decimal import Decimal
 
+from constance import settings
 from constance.base import Config
 
 
@@ -77,3 +78,18 @@ class StorageTestsMixin:
         self.assertEqual(self.config.DATE_VALUE, date(2001, 12, 20))
         self.assertEqual(self.config.TIME_VALUE, time(1, 59, 0))
         self.assertEqual(self.config.TIMEDELTA_VALUE, timedelta(days=1, hours=2, minutes=3))
+
+    def test_backend_retrieves_multiple_values(self):
+        # Check corner cases such as falsy values
+        self.config.INT_VALUE = 0
+        self.config.BOOL_VALUE = False
+        self.config.STRING_VALUE = ''
+
+        values = dict(self.config._backend.mget(settings.CONFIG))
+        self.assertEqual(values['INT_VALUE'], 0)
+        self.assertEqual(values['BOOL_VALUE'], False)
+        self.assertEqual(values['STRING_VALUE'], '')
+
+    def test_backend_does_not_return_none_values(self):
+        result = dict(self.config._backend.mget(settings.CONFIG))
+        self.assertEqual(result, {})