'That function invokes the runshell command, while mocking
subprocess.call. It returns a 2-tuple with:
- The command line list
- The content of the file pointed by environment PGPASSFILE, or None.'

def _run_it(self, dbinfo):

    def _mock_subprocess_call(*args):
        self.subprocess_args = list(*args)
        if ('PGPASSFILE' in os.environ):
            with open(os.environ['PGPASSFILE'], 'r') as f:
                self.pgpass = f.read().strip()
        else:
            self.pgpass = None
        return 0
    self.subprocess_args = None
    self.pgpass = None
    with mock.patch('subprocess.call', new=_mock_subprocess_call):
        DatabaseClient.runshell_db(dbinfo)
    return (self.subprocess_args, self.pgpass)
