Cache.set preserves key order when saving dicts (#9206)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>

AUTHORS

@@ -76,6 +76,7 @@ Christopher Gilling
 Claire Cecil
 Claudio Madotto
 CrazyMerlyn
+Cristian Vera
 Cyrus Maden
 Damian Skrzypczak
 Daniel Grana

changelog/9205.improvement.rst

@@ -0,0 +1 @@
+:meth:`pytest.Cache.set` now preserves key order when saving dicts.

src/_pytest/cacheprovider.py

@@ -193,7 +193,7 @@ class Cache:
             return
         if not cache_dir_exists_already:
             self._ensure_supporting_files()
-        data = json.dumps(value, indent=2, sort_keys=True)
+        data = json.dumps(value, indent=2)
         try:
             f = path.open("w")
         except OSError:

testing/test_cacheprovider.py

@@ -1210,6 +1210,17 @@ def test_gitignore(pytester: Pytester) -> None:
     assert gitignore_path.read_text(encoding="UTF-8") == "custom"
 
 
+def test_preserve_keys_order(pytester: Pytester) -> None:
+    """Ensure keys order is preserved when saving dicts (#9205)."""
+    from _pytest.cacheprovider import Cache
+
+    config = pytester.parseconfig()
+    cache = Cache.for_config(config, _ispytest=True)
+    cache.set("foo", {"z": 1, "b": 2, "a": 3, "d": 10})
+    read_back = cache.get("foo", None)
+    assert list(read_back.items()) == [("z", 1), ("b", 2), ("a", 3), ("d", 10)]
+
+
 def test_does_not_create_boilerplate_in_existing_dirs(pytester: Pytester) -> None:
     from _pytest.cacheprovider import Cache