add testing for uncachable marking

src/pip/_internal/index/collector.py

@@ -639,6 +639,8 @@ def collect_links(self, project_name):
         # We want to filter out anything that does not have a secure origin.
         url_locations = [
             link for link in itertools.chain(
+                # Mark PyPI indices as "uncacheable" -- this will avoid caching
+                # the result of parsing the page for links.
                 (Link(url, uncacheable=True) for url in index_url_loc),
                 (Link(url) for url in fl_url_loc),
             )

tests/unit/test_collector.py

@@ -576,13 +576,14 @@ def test_fetch_page(self, mock_get_html_response):
         fake_response = make_fake_html_response(url)
         mock_get_html_response.return_value = fake_response
 
-        location = Link(url)
+        location = Link(url, uncacheable=True)
         link_collector = make_test_link_collector()
         actual = link_collector.fetch_page(location)
 
         assert actual.content == fake_response.content
         assert actual.encoding is None
         assert actual.url == url
+        assert actual.uncacheable_links == location.uncacheable
 
         # Also check that the right session object was passed to
         # _get_html_response().
@@ -607,8 +608,12 @@ def test_collect_links(self, caplog, data):
 
         assert len(actual.find_links) == 1
         check_links_include(actual.find_links, names=['packages'])
+        # Check that find-links URLs are not marked as cacheable.
+        assert not actual.find_links[0].uncacheable
 
         assert actual.project_urls == [Link('https://pypi.org/simple/twine/')]
+        # Check that index URLs are always marked as uncacheable.
+        assert actual.project_urls[0].uncacheable
 
         expected_message = dedent("""\
         1 location(s) to search for versions of twine: