tests/silenttestrunner.py

phabricator: use Phabricator's last node information

This makes it more strict when checking whether or not we should update a
Differential Revision. For example,

  a) Alice updates D1 to content 1.
  b) Bob updates D1 to content 2.
  c) Alice tries to update D1 to content 1.

Previously, `c)` will do nothing because `phabsend` detects the patch is not
changed. A more correct behavior is to override Bob's update here, hence the
patch.

This also makes it possible to return a reaonsable "last node" when there is
no tags but only `Differential Revision` commit messages.

Test Plan:
```
for i in A B C; do echo $i > $i; hg ci -m $i -A $i; done

hg phabsend 0::
# D40: created
# D41: created
# D42: created

echo 3 >> C; hg amend; hg phabsend .
# D42: updated

hg tag --local --hidden -r 2 -f D42
# move tag to the previous version

hg phabsend .
# D42: skipped (previously it would be "updated")

rm -rf .hg; hg init
hg phabread --stack D42 | hg import -
hg phabsend .
# D42: updated
hg tag --local --remove D42
hg commit --amend
hg phabsend .
# D42: updated (no new diff uploaded, previously it will upload a new diff)
```

The old diff object is now returned, which could be useful in the next
patch.

Differential Revision: https://phab.mercurial-scm.org/D121

from __future__ import absolute_import, print_function
import os
import sys
import unittest

def main(modulename):
    '''run the tests found in module, printing nothing when all tests pass'''
    module = sys.modules[modulename]
    suite = unittest.defaultTestLoader.loadTestsFromModule(module)
    results = unittest.TestResult()
    suite.run(results)
    if results.errors or results.failures:
        for tc, exc in results.errors:
            print('ERROR:', tc)
            print()
            sys.stdout.write(exc)
        for tc, exc in results.failures:
            print('FAIL:', tc)
            print()
            sys.stdout.write(exc)
        sys.exit(1)

if os.environ.get('SILENT_BE_NOISY'):
    main = unittest.main