depot_tools: add test_api to infra_paths recipe module

recipe_modules/infra_paths/api.py

 # Copyright 2016 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.
 
 from recipe_engine import recipe_api
+from recipe_engine.config_types import Path, NamedBasePath
 
 
 class InfraPathsApi(recipe_api.RecipeApi):
   def get_config_defaults(self):
     return {
       'PLATFORM': self.m.platform.name,
       'CURRENT_WORKING_DIR': self.m.path['cwd'],
       'ROOT': self.m.path['root'],
     }
 
   def __init__(self, **kwargs):
     super(InfraPathsApi, self).__init__(**kwargs)
     self._config_set = False
 
   def _lazy_set_config(self):
     if self._config_set:
       return
     self._config_set = True
 
     path_config = self.m.properties.get('path_config')
     if path_config in ('kitchen',):
       self.set_config(path_config)
     else:
       self.set_config('buildbot')
 
+    for path in self._test_data.get('exists', []):
+      assert isinstance(path.base, NamedBasePath)
+      self.m.path.mock_add_paths(self[path.base.name].join(*path.pieces))
+
   def __getitem__(self, name):
     self._lazy_set_config()
     return self.c.paths[name]