tests: target Python 3.8 as the minimum Python version

This version is already two releases out of support, but is "only" 7
years old so is probably still being used in the real world. Document
this version along with some other testing dependencies.  Remove code
support for earlier versions. Disable ruff checks that need a newer
version.

docs/INTERNALS.md

@@ -64,6 +64,19 @@ these or later versions:
 - perl           5.8 (2002-07-19), on Windows: 5.22 (2015-06-01)
 - Visual Studio  2010 10.0 (2010-04-12 - 2020-07-14)
 
+## Testing
+
+Certain tests require the following packages to operate. In some cases, tests
+that do not find the necessary requirements are automatically skipped.
+
+- OpenSSL        (see above)
+- nghttp2        (see above)
+- OpenSSH
+- perl           (see above)
+- pytest
+- Python         3.8 (2019-10-14)
+- stunnel
+
 ## Library Symbols
 
 All symbols used internally in libcurl must use a `Curl_` prefix if they are

scripts/pythonlint.sh

@@ -29,9 +29,11 @@
 
 set -eu
 
-ruff check --extend-select=B007,B016,C405,C416,COM818,D200,D213,D204,D401,\
+ruff check --target-version=py38 \
+--extend-select=B007,B016,C405,C416,COM818,D200,D213,D204,D401,\
 D415,FURB129,N818,PERF401,PERF403,PIE790,PIE808,PLW0127,Q004,RUF010,SIM101,\
 SIM117,SIM118,TRY400,TRY401,RET503,RET504,UP004,B018,B904,RSE102,RET505,I001 \
+--ignore=FA100 \
 "$@"
 # Checks that are in preview only, since --preview otherwise turns them all on
-ruff check --preview --select=E301,E302,E303,E304,E305,E306,E502 "$@"
+ruff check --target-version=py38 --preview --select=E301,E302,E303,E304,E305,E306,E502 "$@"

tests/dictserver.py

@@ -25,8 +25,6 @@
 #
 """DICT server."""
 
-from __future__ import absolute_import, division, print_function, unicode_literals
-
 import argparse
 import logging
 import os

tests/http/testenv/ports.py

@@ -25,8 +25,7 @@
 import logging
 import os
 import socket
-from collections.abc import Callable
-from typing import Dict
+from typing import Callable, Dict
 
 from filelock import FileLock
 

tests/negtelnetserver.py

@@ -22,22 +22,15 @@
 #
 """A telnet server which negotiates."""
 
-from __future__ import absolute_import, division, print_function, unicode_literals
-
 import argparse
 import logging
 import os
 import socket
+import socketserver
 import sys
 
 from util import ClosingFileHandler
 
-if sys.version_info.major >= 3:
-    import socketserver
-else:
-    import SocketServer as socketserver
-
-
 log = logging.getLogger(__name__)
 HOST = "localhost"
 IDENT = "NTEL"