Add logs for update_engine and image_to_live to test artifacts.

lib/cros_build_lib_unittest.py

Index: lib/cros_build_lib_unittest.py
diff --git a/lib/cros_build_lib_unittest.py b/lib/cros_build_lib_unittest.py
index bb3f9d6e4e2d3ba734ad800e6b8c30e4a74b0237..293bff15ab004515c9ddac04f5c5bbbd2b4e105a 100755
--- a/lib/cros_build_lib_unittest.py
+++ b/lib/cros_build_lib_unittest.py
@@ -6,6 +6,8 @@
 
 """Unit tests for cros_build_lib."""
 
+import os
+import tempfile
 import unittest
 
 import cros_build_lib
@@ -87,6 +89,20 @@ class CrosBuildLibTest(unittest.TestCase):
                                        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()