[Predator] Add local cache for get command output.

appengine/findit/common/test/cache_decorator_test.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import __builtin__
+import mock
+import os
 import pickle
 import zlib
 
 from google.appengine.api import memcache
 
 from testing_utils import testing
 
 from common import cache_decorator
 
 
@@ skipping 140 matching lines @@
         return self.url + '/' + path
 
     a1 = A('http://test', 3)
     self.assertEqual('http://test/p1', a1.Func('p1'))
     self.assertEqual('http://test/p1', a1.Func('p1'))
     self.assertEqual(1, a1.runs)
 
     a2 = A('http://test', 5)
     self.assertEqual('http://test/p1', a2.Func('p1'))
     self.assertEqual(0, a2.runs)
+
+  def testLocalCacher(self):
+    fake_dir = 'fake_dir'
+    cacher = cache_decorator.LocalCacher(cache_dir=fake_dir)
+    def _MockPathExists(path, *_):
+      return False if path == os.path.join(
+          fake_dir, 'uncached_key') else True
+    self.mock(os.path, 'exists', _MockPathExists)
+
+    value = 'value'
+    with mock.patch('__builtin__.open', mock.mock_open(
+        read_data=zlib.compress(pickle.dumps('value')))) as m:
+      cacher.Set('a', 'b')
+      m.assert_called_once_with(os.path.join(fake_dir, 'a'), 'wb')
+      self.assertEqual(value, cacher.Get('key'))
+      self.assertIsNone(cacher.Get('uncached_key'))