Wait for the make_expectations.py process to finish before checking return code.

tools/perf_expectations/tests/perf_expectations_unittest.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Verify perf_expectations.json can be loaded using simplejson.
 
 perf_expectations.json is a JSON-formatted file.  This script verifies
 that simplejson can load it correctly.  It should catch most common
@@ skipping 132 matching lines @@
       # tools/buildbot/scripts/master/log_parser.py should have a matching
       # regular expression.
       if not re.match(r"^([\w\.-]+)/([\w\.-]+)/([\w\.-]+)/([\w\.-]+)$", key):
         bad_keys.append(key)
     if len(bad_keys) > 0:
       msg = "perf expectations keys in bad format, expected a/b/c/d"
       raise Exception("%s: %s" % (msg, bad_keys))
 
   def testNoUpdatesNeeded(self):
     p = subprocess.Popen([MAKE_EXPECTATIONS, '-s'], stdout=subprocess.PIPE)
+    p.wait();
     self.assertEqual(p.returncode, 0, msg='Expectations has pending updates!')
 
   def testConfigFile(self):
     # Test that the config file can be parsed as JSON.
     config = LoadJsonFile(CONFIG_JSON)
     # Require the following keys.
     if 'base_url' not in config:
       raise Exception('base_url not specified in config file')
     if 'perf_file' not in config:
       raise Exception('perf_file not specified in config file')
 
 
 if __name__ == '__main__':
   unittest.main()