def METHOD_NAME(self, content):
    output = None
    try:
        testcmd = ['promtool', 'check', 'metrics']
        process = subprocess.Popen(testcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.STDOUT, close_fds=True)
        output = process.communicate(input=content)
    except subprocess.CalledProcessError as exc:
        raise AssertionError('%s failed (%d): %s' % (testcmd, process.returncode, process.output))
    # commented out because promtool returns 3 because of the "_total" suffix warnings
    #if process.returncode != 0:
    #  raise AssertionError('%s failed (%d): %s' % (testcmd, process.returncode, output))
    for line in output[0].splitlines():
        if line.endswith(b"should have \"_total\" suffix"):
            continue
        raise AssertionError('%s returned an unexpected output. Faulty line is "%s", complete content is "%s"' % (testcmd, line, output))