test parse_header_links via public api (#3061)

* test `parse_header_links` via public api

* add no-link test

* Update tests/test_utils.py

---------

Co-authored-by: Tom Christie <tom@tomchristie.com>

httpx/_models.py

@@ -774,13 +774,13 @@ class Response:
         Returns the parsed header links of the response, if any
         """
         header = self.headers.get("link")
-        ldict = {}
-        if header:
-            links = parse_header_links(header)
-            for link in links:
-                key = link.get("rel") or link.get("url")
-                ldict[key] = link
-        return ldict
+        if header is None:
+            return {}
+
+        return {
+            (link.get("rel") or link.get("url")): link
+            for link in parse_header_links(header)
+        }
 
     @property
     def num_bytes_downloaded(self) -> int:

tests/test_utils.py

@@ -12,7 +12,6 @@ from httpx._utils import (
     get_ca_bundle_from_env,
     get_environment_proxies,
     is_https_redirect,
-    parse_header_links,
     same_origin,
 )
 
@@ -80,7 +79,13 @@ def test_guess_by_bom(encoding, expected):
     ),
 )
 def test_parse_header_links(value, expected):
-    assert parse_header_links(value) == expected
+    all_links = httpx.Response(200, headers={"link": value}).links.values()
+    assert all(link in all_links for link in expected)
+
+
+def test_parse_header_links_no_link():
+    all_links = httpx.Response(200).links
+    assert all_links == {}
 
 
 def test_logging_request(server, caplog):