Add unit test to clean_caches()

client/run_isolated.py

 #!/usr/bin/env python
 # Copyright 2012 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.
 
 """Runs a command with optional isolated input/output.
 
 Despite name "run_isolated", can run a generic non-isolated command specified as
 args.
 
@@ skipping 806 matching lines @@
       pins={
         'client_package': {
           'package_name': client.package_name,
           'version': client.instance_id,
         },
         'packages': package_pins,
       })
 
 
 def clean_caches(options, isolate_cache, named_cache_manager):
-  """Trims isolated and named caches."""
-  # Which cache to trim first? Which of caches was used least recently?
+  """Trims isolated and named caches.
+
+  The goal here is to coherently trim both caches, deleting older items
+  independent of which container they belong to.
+  """
+  # TODO(maruel): Trim CIPD cache the same way.
+  total = 0
   with named_cache_manager.open():
     oldest_isolated = isolate_cache.get_oldest()
     oldest_named = named_cache_manager.get_oldest()
     trimmers = [
       (
         isolate_cache.trim,
         isolate_cache.get_timestamp(oldest_isolated) if oldest_isolated else 0,
       ),
       (
         lambda: named_cache_manager.trim(options.min_free_space),
         named_cache_manager.get_timestamp(oldest_named) if oldest_named else 0,
       ),
     ]
     trimmers.sort(key=lambda (_, ts): ts)
+    # TODO(maruel): This is incorrect, we want to trim 'items' that are strictly
+    # the oldest independent of in which cache they live in. Right now, the
+    # cache with the oldest item pays the price.
     for trim, _ in trimmers:
-      trim()
+      total += trim()
   isolate_cache.cleanup()
+  return total
 
 
 def create_option_parser():
   parser = logging_utils.OptionParserWithLogging(
       usage='%prog <options> [command to run or extra args]',
       version=__version__,
       log_file=RUN_ISOLATED_LOG_FILE)
   parser.add_option(
       '--clean', action='store_true',
       help='Cleans the cache, trimming it necessary and remove corrupted items '
@@ skipping 195 matching lines @@
     return 1
 
 
 if __name__ == '__main__':
   subprocess42.inhibit_os_error_reporting()
   # Ensure that we are always running with the correct encoding.
   fix_encoding.fix_encoding()
   file_path.enable_symlink()
 
   sys.exit(main(sys.argv[1:]))