depot_tools/recipe_modules/tryserver/test_api.py

from recipe_engine import recipe_test_api

class TryserverTestApi(recipe_test_api.RecipeTestApi):
  def patch_content(self):
    return self.m.raw_io.output(
        'fake patch.diff content (line 1)\n'
        'fake patch.diff content (line 2)\n')