Allow skipping the testcase that requires network

[s-t-e-v-e-n-k]

Not all test environments allow internet access, and one of the testcases relies on it by downloading an image over HTTPS. Add a check for a environment variable to skip it.

If 'NONET" is not descriptive enough, I'm happy to update it to 'SKIP_NETWORK' or something else.

[jim-easterbrook]

Good idea. I'd really like to automate network detection instead of relying on an environment variable though. I'll investigate what's possible.

[jim-easterbrook]

Something like this should do the job:

# Source - https://stackoverflow.com/a/29854274
# Posted by Ivelin, modified by community. See post 'Timeline' for change history
# Retrieved 2026-03-16, License - CC BY-SA 4.0

import http.client

def have_internet():
    conn = http.client.HTTPSConnection("8.8.8.8", timeout=5)
    try:
        conn.request("HEAD", "/")
        return True
    except Exception:
        return False
    finally:
        conn.close()