Mocking and testing a function which returns text from an url

I have a function which takes an url and returns the text from this url.

def extract_raw_text_from_url(url, set_parser='lxml'):

    try:
        req = Request(url, headers={'User-Agent': 'Mozilla/5.0'})  # Set user agent as Mozilla. Otherwise: Error 403
        source = urlopen(req).read()  # Return source code

        parser = set_parser
        soup = bs.BeautifulSoup(source, parser)  # create beautiful soup object

        text = soup.get_text()  # get text of websites

    except (ValueError): # ToDo: Why urllib.error.URLError is unknown? I want to include it in exception! Works in Colab!
        text = []

    return text

How do I properly test this function? Since I think it's bad practise to make a request each time I run the test, I think it would be a nice idea to mock the result.

Any idea how to do this? I am using pytest but I'm still a beginner.