test function with Google App Engine `files` api

Question

I have a function that uses the Google Blobstore API, and here's a degenerate case:

#!/usr/bin/python
from google.appengine.ext import testbed

def foo():
    from google.appengine.api import files
    blob_filename = files.blobstore.create(mime_type='text/plain')
    with files.open(blob_filename, 'a') as googfile:
        googfile.write("Test data")

    files.finalize(blob_filename)

tb = testbed.Testbed()
tb.activate()
tb.init_blobstore_stub()

foo() # in reality, I'm a function called from a 'faux client'
      # in a unittest testcase.

The error this generates is:

Traceback (most recent call last):
  File "e.py", line 18, in 
    foo() # in reality, I'm a function called from a 'faux client'
  File "e.py", line 8, in foo
    blob_filename = files.blobstore.create(mime_type='text/plain')
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/files/blobstore.py", line 68, in create
    return files._create(_BLOBSTORE_FILESYSTEM, params=params)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/files/file.py", line 491, in _create
    _make_call('Create', request, response)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/files/file.py", line 230, in _make_call
    rpc = _create_rpc(deadline=deadline)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/files/file.py", line 213, in _create_rpc
    return apiproxy_stub_map.UserRPC('file', deadline)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 393, in __init__
    self.__rpc = CreateRPC(service, stubmap)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 67, in CreateRPC
    assert stub, 'No api proxy found for service "%s"' % service
AssertionError: No api proxy found for service "file"

I don't want to have to modify foo in order to be able to test it. Is there a way to make foo work as expected (i.e. create the given file) in Google App Engine's unit tests?

I would expect to be able to do this with Google's API Proxy, but I don't understand it well enough to figure it out on my own.

I'd be grateful for your thoughts and suggestions.

Thanks for reading.

Answer 1

It seems like testbed.init_blobstore_stub() is outdated, because dev_appserver inits blobstore stubs differently. Here is my implementation of init_blobstore_stub that allows you to write to and read from blobstore in your tests.

from google.appengine.ext import testbed
from google.appengine.api.blobstore import blobstore_stub, file_blob_storage
from google.appengine.api.files import file_service_stub

class TestbedWithFiles(testbed.Testbed):

    def init_blobstore_stub(self):
        blob_storage = file_blob_storage.FileBlobStorage('/tmp/testbed.blobstore',
                                                testbed.DEFAULT_APP_ID)
        blob_stub = blobstore_stub.BlobstoreServiceStub(blob_storage)
        file_stub = file_service_stub.FileServiceStub(blob_storage)
        self._register_stub('blobstore', blob_stub)
        self._register_stub('file', file_stub)

# Your code...
def foo():
    from google.appengine.api import files
    blob_filename = files.blobstore.create(mime_type='text/plain')
    with files.open(blob_filename, 'a') as googfile:
        googfile.write("Test data")

    files.finalize(blob_filename)

tb = TestbedWithFiles()
tb.activate()
tb.init_blobstore_stub()

foo()

Answer 2

I don't know if it was added later to the SDK, but using Testbed.init_files_stub should fix it:

tb = testbed.Testbed()
tb.activate()
tb.init_blobstore_stub()
tb.init_files_stub()