Code review comment for lp:~toshio/bzr/allow-dirty-patches

I thought I'd add a test for this as patch pilot, so I put in this one based on bug 502076:

    def test_parse_leading_noise(self):
        """Parse a valid patch header"""
        # https://bugs.edge.launchpad.net/bzr/+bug/502076
        lines = ["diff -pruN commands.py",
            "--- orig/commands.py"
            "+++ mod/dommands.py"]
        bits = parse_patch(iter(lines), allow_dirty=True)

however this fails with

Traceback (most recent call last):
  File "/home/mbp/lib/python/testtools/runtest.py", line 128, in _run_user
    return fn(*args)
  File "/home/mbp/lib/python/testtools/testcase.py", line 369, in _run_test_method
    testMethod()
  File "/home/mbp/bzr/502076-dirty-patches/bzrlib/tests/test_patches.py", line 63, in test_parse_leading_noise
    bits = parse_patch(iter(lines), allow_dirty=True)
  File "/home/mbp/bzr/502076-dirty-patches/bzrlib/patches.py", line 364, in parse_patch
    (orig_name, mod_name) = get_patch_names(iter_lines)
  File "/home/mbp/bzr/502076-dirty-patches/bzrlib/patches.py", line 76, in get_patch_names
    raise MalformedPatchHeader("No orig name", line)
MalformedPatchHeader: Malformed patch header. No orig name
'diff -pruN commands.py'

Can someone tell me what format this is supposed to be parsing, or what's wrong with that test?