Add logs for update_engine and image_to_live to test artifacts.

lib/cros_build_lib_unittest.py

 #!/usr/bin/python
 #
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Unit tests for cros_build_lib."""
 
+import os
+import tempfile
 import unittest
 
 import cros_build_lib
 
 class CrosBuildLibTest(unittest.TestCase):
   """Test class for cros_build_lib."""
 
   def testRunCommandSimple(self):
     """Test that RunCommand can run a simple successful command."""
     result = cros_build_lib.RunCommand(['ls'],
@@ skipping 61 matching lines @@
   def testRunCommandCaptureOutput(self):
     """Test that RunCommand can capture stdout if a command succeeds."""
 
     result = cros_build_lib.RunCommand(['echo', '-n', 'Hi'],
                                        # Keep the test quiet options
                                        print_cmd=False,
                                        redirect_stdout=True,
                                        redirect_stderr=True)
     self.assertEqual(result, 'Hi')
 
+  def testRunCommandLogToFile(self):
+    """Test that RunCommand can log output to a file correctly."""
+    log_file = tempfile.mktemp()
+    cros_build_lib.RunCommand(['echo', '-n', 'Hi'],
+                               # Keep the test quiet options
+                               print_cmd=False,
+                               # Test specific options
+                               log_to_file=log_file)
+    log_fh = open(log_file)
+    log_data = log_fh.read()
+    self.assertEquals('Hi', log_data)
+    log_fh.close()
+    os.remove(log_file)
+
 
 if __name__ == '__main__':
   unittest.main()