Refactor infra git libs and testing.

infra/libs/git2/util.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+from cStringIO import StringIO
+
+
+class _Invalid(object):
+  def __call__(self, *_args, **_kwargs):
+    return self
+
+  def __getattr__(self, _key):
+    return self
+
+  def __eq__(self, _other):
+    return False
+
+  def __ne__(self, _other):  # pylint: disable=R0201
+    return True
+
+INVALID = _Invalid()
+
+
+class CalledProcessError(Exception):
+  """Almost like subprocess.CalledProcessError, but also captures stderr,
+  and gives prettier error messages.
+  """
+  def __init__(self, returncode, cmd, stdout, stderr):
+    super(CalledProcessError, self).__init__()
+    self.returncode = returncode
+    self.cmd = cmd
+    self.stdout = stdout
+    self.stderr = stderr
+
+  def __str__(self):
+    msg = StringIO()
+
+    suffix = ':' if self.stderr or self.stdout else '.'
+    print >> msg, (
+        "Command %r returned non-zero exit status %d%s"
+        % (self.cmd, self.returncode, suffix)
+    )
+
+    def indent_data(banner, data):
+      print >> msg, banner, '=' * 40
+      msg.writelines('  ' + l for l in data.splitlines(True))
+
+    if self.stdout:
+      indent_data('STDOUT', self.stdout)
+
+    if self.stderr:
+      if self.stdout:
+        print >> msg
+      indent_data('STDERR', self.stderr)
+
+    r = msg.getvalue()
+    if r[-1] != '\n':
+      r += '\n'
+    return r
+