Add unit test to clean_caches()

client/tests/isolateserver_test.py

 #!/usr/bin/env python
 # Copyright 2013 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 # pylint: disable=W0212,W0223,W0231,W0613
 
 import base64
 import hashlib
 import json
@@ skipping 1318 matching lines @@
     # Min free disk: 1000 bytes.
     self._policies = isolateserver.CachePolicies(100, 1000, 2)
     def get_free_space(p):
       self.assertEqual(p, self.tempdir)
       return self._free_disk
     self.mock(file_path, 'get_free_space', get_free_space)
     # TODO(maruel): Test the following.
     #cache.touch()
 
   def get_cache(self):
-    return isolateserver.DiskCache(self.tempdir, self._policies, self._algo)
+    return isolateserver.DiskCache(
+        self.tempdir, self._policies, self._algo, trim=True)
 
   def to_hash(self, content):
     return self._algo(content).hexdigest(), content
 
   def test_read_evict(self):
     self._free_disk = 1100
     h_a = self.to_hash('a')[0]
     with self.get_cache() as cache:
       cache.write(h_a, 'a')
       with cache.getfileobj(h_a) as f:
@@ skipping 121 matching lines @@
 
 
 if __name__ == '__main__':
   fix_encoding.fix_encoding()
   if '-v' in sys.argv:
     unittest.TestCase.maxDiff = None
   logging.basicConfig(
       level=(logging.DEBUG if '-v' in sys.argv else logging.CRITICAL))
   clear_env_vars()
   unittest.main()