Add script that allow users to preload examples for offline testing

setuptools/tests/config/downloads/.gitignore

@@ -1,2 +1,4 @@
 *
 !.gitignore
+!__init__.py
+!preload.py

setuptools/tests/config/downloads/preload.py

@@ -0,0 +1,18 @@
+"""This file can be used to preload files needed for testing.
+
+For example you can use::
+
+    cd setuptools/tests/config
+    python -m downloads.preload setupcfg_examples.txt
+
+to make sure the `setup.cfg` examples are downloaded before starting the tests.
+"""
+import sys
+from pathlib import Path
+
+from . import retrieve_file, urls_from_file
+
+
+if __name__ == "__main__":
+    urls = urls_from_file(Path(sys.argv[1]))
+    list(map(retrieve_file, urls))