PytestUnknownMarkWarning: Unknown pytest.mark.xxx - is this a typo?

I have a file called test.py with the following code:

import pytest

@pytest.mark.webtest
def test_http_request():
    pass

class TestClass:
    def test_method(self):
        pass

pytest -s test.py passed but gave the following warnings:

pytest -s test.py
=============================== test session starts ============================
platform linux -- Python 3.7.3, pytest-5.2.4, py-1.8.0, pluggy-0.13.1
rootdir: /home/user
collected 2 items

test.py ..

=============================== warnings summary ===============================
anaconda3/lib/python3.7/site-packages/_pytest/mark/structures.py:325
  ~/anaconda3/lib/python3.7/site-packages/_pytest/mark/structures.py:325:
    PytestUnknownMarkWarning: Unknown pytest.mark.webtest - is this a typo?  You can register
    custom marks to avoid this warning - for details, see https://docs.pytest.org/en/latest/mark.html
    PytestUnknownMarkWarning,

-- Docs: https://docs.pytest.org/en/latest/warnings.html
=============================== 2 passed, 1 warnings in 0.03s ===================

Environment: Python 3.7.3, pytest 5.2.4, anaconda3

What is the best way to get rid of the warning message?

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