#!/usr/bin/env python
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"""Unit test for Google Test's break-on-failure mode.

A user can ask Google Test to seg-fault when an assertion fails, using
either the GTEST_BREAK_ON_FAILURE environment variable or the
--gtest_break_on_failure flag.  This script tests such functionality
by invoking gtest_break_on_failure_unittest_ (a program written with
Google Test) with different environments and command line flags.
"""

__author__ = 'wan@google.com (Zhanyong Wan)'

import gtest_test_utils
import os
import signal
import sys
import unittest


# Constants.

# The environment variable for enabling/disabling the break-on-failure mode.
BREAK_ON_FAILURE_ENV_VAR = 'GTEST_BREAK_ON_FAILURE'

# The command line flag for enabling/disabling the break-on-failure mode.
BREAK_ON_FAILURE_FLAG = 'gtest_break_on_failure'

# Path to the gtest_break_on_failure_unittest_ program.
EXE_PATH = os.path.join(gtest_test_utils.GetBuildDir(),
                        'gtest_break_on_failure_unittest_');


# Utilities.

def SetEnvVar(env_var, value):
  """Sets an environment variable to a given value; unsets it when the
  given value is None.
  """

  if value is not None:
    os.environ[env_var] = value
  elif env_var in os.environ:
    del os.environ[env_var]


def Run(command):
  """Runs a command; returns 1 if it was killed by a signal, or 0 otherwise.
  """

  exit_code = os.system(command)
  # On Unix-like systems, the lowest 8 bits of the exit code is the
  # signal number that killed the process (or 0 if it wasn't killed by
  # a signal).
  return (exit_code & 255) != 0


# The unit test.

class GTestBreakOnFailureUnitTest(unittest.TestCase):
  """Tests using the GTEST_BREAK_ON_FAILURE environment variable or
  the --gtest_break_on_failure flag to turn assertion failures into
  segmentation faults.
  """

  def RunAndVerify(self, env_var_value, flag_value, expect_seg_fault):
    """Runs gtest_break_on_failure_unittest_ and verifies that it does
    (or does not) have a seg-fault.

    Args:
      env_var_value:    value of the GTEST_BREAK_ON_FAILURE environment
                        variable; None if the variable should be unset.
      flag_value:       value of the --gtest_break_on_failure flag;
                        None if the flag should not be present.
      expect_seg_fault: 1 if the program is expected to generate a seg-fault;
                        0 otherwise.
    """

    SetEnvVar(BREAK_ON_FAILURE_ENV_VAR, env_var_value)

    if env_var_value is None:
      env_var_value_msg = ' is not set'
    else:
      env_var_value_msg = '=' + env_var_value

    if flag_value is None:
      flag = ''
    elif flag_value == '0':
      flag = ' --%s=0' % BREAK_ON_FAILURE_FLAG
    else:
      flag = ' --%s' % BREAK_ON_FAILURE_FLAG

    command = EXE_PATH + flag

    if expect_seg_fault:
      should_or_not = 'should'
    else:
      should_or_not = 'should not'

    has_seg_fault = Run(command)

    SetEnvVar(BREAK_ON_FAILURE_ENV_VAR, None)

    msg = ('when %s%s, an assertion failure in "%s" %s cause a seg-fault.' %
           (BREAK_ON_FAILURE_ENV_VAR, env_var_value_msg, command, should_or_not))
    self.assert_(has_seg_fault == expect_seg_fault, msg)

  def testDefaultBehavior(self):
    """Tests the behavior of the default mode."""

    self.RunAndVerify(env_var_value=None,
                      flag_value=None,
                      expect_seg_fault=0)

  def testEnvVar(self):
    """Tests using the GTEST_BREAK_ON_FAILURE environment variable."""

    self.RunAndVerify(env_var_value='0',
                      flag_value=None,
                      expect_seg_fault=0)
    self.RunAndVerify(env_var_value='1',
                      flag_value=None,
                      expect_seg_fault=1)

  def testFlag(self):
    """Tests using the --gtest_break_on_failure flag."""

    self.RunAndVerify(env_var_value=None,
                      flag_value='0',
                      expect_seg_fault=0)
    self.RunAndVerify(env_var_value=None,
                      flag_value='1',
                      expect_seg_fault=1)

  def testFlagOverridesEnvVar(self):
    """Tests that the flag overrides the environment variable."""

    self.RunAndVerify(env_var_value='0',
                      flag_value='0',
                      expect_seg_fault=0)
    self.RunAndVerify(env_var_value='0',
                      flag_value='1',
                      expect_seg_fault=1)
    self.RunAndVerify(env_var_value='1',
                      flag_value='0',
                      expect_seg_fault=0)
    self.RunAndVerify(env_var_value='1',
                      flag_value='1',
                      expect_seg_fault=1)


if __name__ == '__main__':
  gtest_test_utils.Main()