capture logging in a few tests

this could probably be made more general,
but these were the two places I noticed log output.

IPython/html/tests/test_notebookapp.py

@@ -11,6 +11,7 b''
 # Imports
 #-----------------------------------------------------------------------------
 
+import logging
 import os
 from tempfile import NamedTemporaryFile
 
@@ -31,7 +32,7 b' def test_help_output():'
     tt.help_all_output_test('notebook')
 
 def test_server_info_file():
-    nbapp = NotebookApp(profile='nbserver_file_test')
+    nbapp = NotebookApp(profile='nbserver_file_test', log=logging.getLogger())
     def get_servers():
         return list(notebookapp.list_running_servers(profile='nbserver_file_test'))
     nbapp.initialize(argv=[])

IPython/nbconvert/postprocessors/tests/test_pdf.py

@@ -14,6 +14,7 b' Module with tests for the PDF post-processor'
 # Imports
 #-----------------------------------------------------------------------------
 
+import logging
 import os
 
 from IPython.testing import decorators as dec
@@ -56,7 +57,7 b' class TestPDF(TestsBase):'
                 f.write(HELLO_WORLD)
 
             # Construct post-processor
-            processor = PDFPostProcessor()
+            processor = PDFPostProcessor(log=logging.getLogger())
             processor.verbose = False
             processor('a.tex')