[iot] testing: verbose log output, adding a new assert (GoogleCloudPlatform#3854)

part of GoogleCloudPlatform#3852

Author: Takashi Matsuo

iot/api-client/mqtt_example/cloudiot_mqtt_example_test.py

@@ -184,6 +184,9 @@ def test_gateway_send_data_for_device(
 
     out, _ = capsys.readouterr()
     assert 'Publishing message 5/5' in out
+    assert 'Received message' in out
+    # We know we sometimes get 'Out of memory' in the output.
+    # We'd like to know when this occurs with verbose log output.
     assert 'Out of memory' not in out  # Indicates could not connect
 
 

iot/api-client/mqtt_example/pytest.ini

@@ -0,0 +1,2 @@
+[pytest]
+addopts = -vv