uploader: fix graph RPC test (#3507)

Summary:
The graph uploader test wasn’t actually covering the blob writing code,
and was set up incorrectly such that the request iterator would throw
when forced.

Test Plan:
The new assertions pass, but fail if the RPC changes are reverted.

wchargin-branch: uploader-graph-write-test

Author: wchargin

tensorboard/uploader/uploader_test.py

@@ -19,6 +19,7 @@
 from __future__ import print_function
 
 import collections
+import itertools
 import os
 
 import grpc
@@ -81,6 +82,12 @@ def _create_mock_client():
         experiment_id="123", url="should not be used!"
     )
     mock_client.CreateExperiment.return_value = fake_exp_response
+    mock_client.GetOrCreateBlobSequence.side_effect = (
+        write_service_pb2.GetOrCreateBlobSequenceResponse(
+            blob_sequence_id="blob%d" % i
+        )
+        for i in itertools.count()
+    )
     return mock_client
 
 
@@ -281,7 +288,6 @@ def test_start_uploading_graphs(self):
         graph_event = event_pb2.Event(
             graph_def=_create_example_graph_bytes(950)
         )
-
         mock_logdir_loader = mock.create_autospec(logdir_loader.LogdirLoader)
         mock_logdir_loader.get_run_events.side_effect = [
             {
@@ -302,6 +308,13 @@ def test_start_uploading_graphs(self):
             uploader.start_uploading()
         self.assertEqual(1, mock_client.CreateExperiment.call_count)
         self.assertEqual(10, mock_client.WriteBlob.call_count)
+        for (i, call) in enumerate(mock_client.WriteBlob.call_args_list):
+            requests = list(call[0][0])
+            data = b"".join(r.data for r in requests)
+            self.assertEqual(data, graph_event.graph_def)
+            self.assertEqual(
+                set(r.blob_sequence_id for r in requests), {"blob%d" % i},
+            )
         self.assertEqual(0, mock_rate_limiter.tick.call_count)
         self.assertEqual(10, mock_blob_rate_limiter.tick.call_count)