Pretty-print builtin frozendict in assertion diffs

AUTHORS

@@ -497,6 +497,7 @@ Tim Strazny
 TJ Bruno
 Tobias Diez
 Tobias Petersen
+Toluwalase Akinyemi
 Tom Dalton
 Tom Most
 Tom Viner

changelog/15172.bugfix.rst

@@ -0,0 +1 @@
+Assertion diffs now pretty-print the built-in :class:`frozendict` (Python 3.15+) across multiple lines, the same way :class:`dict` is displayed.

src/_pytest/_io/pprint.py

@@ -29,6 +29,7 @@
 from collections.abc import Iterator
 import dataclasses as _dataclasses
 import re
+import sys
 import types as _types
 from typing import Any
 
@@ -229,6 +230,10 @@ def _pprint_ordered_dict(
 
     _dispatch[_collections.OrderedDict.__repr__] = _pprint_ordered_dict
 
+    if sys.version_info >= (3, 15):
+        # frozendict's repr has the same shape as OrderedDict's: Name({...})
+        _dispatch[frozendict.__repr__] = _pprint_ordered_dict  # noqa: F821
+
     def _pprint_list(
         self,
         object: Any,

testing/io/test_pprint.py

@@ -9,6 +9,7 @@
 from collections import UserList
 from collections import UserString
 from dataclasses import dataclass
+import sys
 import textwrap
 from types import MappingProxyType
 from types import SimpleNamespace
@@ -651,6 +652,32 @@ class MyNamespace(SimpleNamespace):
     assert pp.pformat(MyNamespace(one=1)) == "MyNamespace(\n    one=1,\n)"
 
 
+@pytest.mark.skipif(
+    sys.version_info < (3, 15), reason="frozendict is a builtin since Python 3.15"
+)
+def test_frozendict() -> None:
+    if sys.version_info >= (3, 15):  # for mypy, which checks against Python 3.10
+        pp = PrettyPrinter()
+        assert pp.pformat(frozendict()) == "frozendict()"  # noqa: F821
+        assert pp.pformat(frozendict({"one": 1, "two": 2})) == textwrap.dedent(  # noqa: F821
+            """\
+            frozendict({
+                'one': 1,
+                'two': 2,
+            })"""
+        )
+
+        class MyFrozenDict(frozendict):  # noqa: F821
+            pass
+
+        assert pp.pformat(MyFrozenDict({"one": 1})) == textwrap.dedent(
+            """\
+            MyFrozenDict({
+                'one': 1,
+            })"""
+        )
+
+
 def test_safe_tuple_sorts_unorderable_pairs() -> None:
     # ``_safe_tuple`` wraps each element of a 2-tuple in ``_safe_key`` so a
     # list of pairs with unorderable elements can be sorted without raising.