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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _run_tox_env(self, env_name, extra_env_vars={}):
 """ Run the specified tox environment. :param env_name: name of the tox environment to run :type env_name: str :param extra_env_vars: additional variables to set in the environment :type extra_env_vars: dict :raises: RuntimeError :returns: combined STDOUT / STDERR :rtype: str """

        projdir = self.projdir
        env = deepcopy(os.environ)
        env['PATH'] = self._fixed_path(projdir)
        env.update(extra_env_vars)
        cmd = [os.path.join(projdir, 'bin', 'tox'), '-e', env_name]
        logger.info(
            'Running tox environment %s: args="%s" cwd=%s '
            'timeout=1800', env_name, ' '.join(cmd), projdir
        )
        res = subprocess.run(
            cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
            cwd=projdir, timeout=1800, env=env
        )
        logger.info('tox process exited %d', res.returncode)
        if res.returncode != 0:
            logger.error(
                'ERROR: tox environment %s exitcode %d',
                env_name, res.returncode
            )
            logger.error(
                'tox output:\n%s', res.stdout.decode()
            )
            res.check_returncode()
        return res.stdout.decode()