Output command line when packager tests fail

- Changed python packaging test to output the command line it ran for
  tests that failed.

Change-Id: I52c06bcec725c9dce7f845ab138cfab29b582201

packager/app/test/packager_app.py

@@ -22,6 +22,9 @@ class PackagerApp(object):
     if platform.system() == 'Windows':
       packager_name += '.exe'
     self.binary = os.path.join(test_env.SCRIPT_DIR, packager_name)
+    # Set this to empty for now in case GetCommandLine() is called before
+    # Package().
+    self.packaging_command_line = ''
     assert os.path.exists(self.binary), ('Please run from output directory, '
                                          'e.g. out/Debug/packager_test.py')
 
@@ -39,4 +42,10 @@ class PackagerApp(object):
     cmd = [self.binary]
     cmd.extend(streams)
     cmd.extend(flags)
+    # Put single-quotes around each entry so that things like '$' signs in
+    # segment templates won't be interpreted as shell variables.
+    self.packaging_command_line = ' '.join(["'%s'" % entry for entry in cmd])
     assert 0 == subprocess.call(cmd)
+
+  def GetCommandLine(self):
+    return self.packaging_command_line

packager/app/test/packager_test.py

@@ -19,6 +19,14 @@ import unittest
 import packager_app
 import test_env
 
+_TEST_FAILURE_COMMAND_LINE_MESSAGE = """
+!!! To reproduce the failure, change the output files to an !!!
+!!! existing directory, e.g. output artifacts to current    !!!
+!!! directory by removing /tmp/something/ in the following  !!!
+!!! command line.                                           !!!
+The test executed the following command line:
+"""
+
 
 class PackagerAppTest(unittest.TestCase):
 
@@ -658,7 +666,11 @@ class PackagerAppTest(unittest.TestCase):
                              stdout=subprocess.PIPE,
                              stderr=subprocess.PIPE)
         output, error = p.communicate()
-        self.fail(output + error)
+        command_line = self.packager.GetCommandLine()
+        failure_message = (output + error + '\n' +
+                           _TEST_FAILURE_COMMAND_LINE_MESSAGE +
+                           command_line)
+        self.fail(failure_message)
 
   # '*.media_info' outputs contain media file names, which is changing for
   # every test run. These needs to be replaced for comparison.