tests/filtertraceback.py

test: use a more verbose output in the test

While debugging some test failure, I released the test never checks if the
relevant changesets were preserved. So I am updating the test from `hg parents`
usage to `hg log -G` with a special template. This increase the area covered by
the test and clarify the test failures.

#!/usr/bin/env python

# Filters traceback lines from stdin.

from __future__ import absolute_import, print_function

import sys

state = 'none'

for line in sys.stdin:
    if state == 'none':
        if line.startswith('Traceback '):
            state = 'tb'

    elif state == 'tb':
        if line.startswith('  File '):
            state = 'file'
            continue

        elif not line.startswith(' '):
            state = 'none'

    elif state == 'file':
        # Ignore lines after "  File "
        state = 'tb'
        continue

    print(line, end='')