Fix dict order assertion output

changelog/13503.bugfix.rst

@@ -0,0 +1,5 @@
+Preserve dictionary insertion order in assertion failure output.
+
+Previously, pytest displayed dictionaries in sorted key order in assertion
+failure messages. This change ensures dictionaries are shown in their original
+insertion order, matching Python’s dict semantics.

src/_pytest/_io/saferepr.py

@@ -1,7 +1,9 @@
 from __future__ import annotations
 
+from collections.abc import Mapping
 import pprint
 import reprlib
+from typing import Any
 
 
 def _try_repr_or_str(obj: object) -> str:
@@ -54,6 +56,9 @@ def __init__(self, maxsize: int | None, use_ascii: bool = False) -> None:
         self.maxsize = maxsize
         self.use_ascii = use_ascii
 
+    def repr_dict(self, x: Mapping[Any, Any], level: int) -> str:
+        return dict.__repr__(x)
+
     def repr(self, x: object) -> str:
         try:
             if self.use_ascii:

src/_pytest/assertion/util.py

@@ -9,7 +9,6 @@
 from collections.abc import Mapping
 from collections.abc import Sequence
 from collections.abc import Set as AbstractSet
-import pprint
 from typing import Any
 from typing import Literal
 from typing import Protocol
@@ -510,7 +509,7 @@ def _compare_eq_dict(
         explanation += [f"Omitting {len(same)} identical items, use -vv to show"]
     elif same:
         explanation += ["Common items:"]
-        explanation += highlighter(pprint.pformat(same)).splitlines()
+        explanation += highlighter(PrettyPrinter().pformat(same)).splitlines()
     diff = {k for k in common if left[k] != right[k]}
     if diff:
         explanation += ["Differing items:"]
@@ -527,7 +526,9 @@ def _compare_eq_dict(
             f"Left contains {len_extra_left} more item{'' if len_extra_left == 1 else 's'}:"
         )
         explanation.extend(
-            highlighter(pprint.pformat({k: left[k] for k in extra_left})).splitlines()
+            highlighter(
+                PrettyPrinter().pformat({k: left[k] for k in extra_left})
+            ).splitlines()
         )
     extra_right = set_right - set_left
     len_extra_right = len(extra_right)
@@ -536,7 +537,9 @@ def _compare_eq_dict(
             f"Right contains {len_extra_right} more item{'' if len_extra_right == 1 else 's'}:"
         )
         explanation.extend(
-            highlighter(pprint.pformat({k: right[k] for k in extra_right})).splitlines()
+            highlighter(
+                PrettyPrinter().pformat({k: right[k] for k in extra_right})
+            ).splitlines()
         )
     return explanation
 
@@ -575,10 +578,10 @@ def _compare_eq_cls(
         explanation.append(f"Omitting {len(same)} identical items, use -vv to show")
     elif same:
         explanation += ["Matching attributes:"]
-        explanation += highlighter(pprint.pformat(same)).splitlines()
+        explanation += highlighter(PrettyPrinter().pformat(same)).splitlines()
     if diff:
         explanation += ["Differing attributes:"]
-        explanation += highlighter(pprint.pformat(diff)).splitlines()
+        explanation += highlighter(PrettyPrinter().pformat(diff)).splitlines()
         for field in diff:
             field_left = getattr(left, field)
             field_right = getattr(right, field)

testing/test_assertion.py

@@ -19,6 +19,27 @@
 import pytest
 
 
+def test_dict_preserves_insertion_order_in_assertion(pytester):
+    pytester.makepyfile(
+        test_sample="""
+        def test_example():
+            a = {
+                "b": "",
+                "a": "",
+                "c": "",
+            }
+            assert a == {}
+        """
+    )
+
+    result = pytester.runpytest()
+    output = result.stdout.str()
+
+    # The dict should be shown in insertion order: b, a, c
+    assert output.index("'b'") < output.index("'a'")
+    assert output.index("'a'") < output.index("'c'")
+
+
 def mock_config(verbose: int = 0, assertion_override: int | None = None):
     class TerminalWriter:
         def _highlight(self, source, lexer="python"):
@@ -209,8 +230,10 @@ def test_pytest_plugins_rewrite_module_names_correctly(
             "hamster.py": "",
             "test_foo.py": """\
                 def test_foo(pytestconfig):
-                    assert pytestconfig.pluginmanager.rewrite_hook.find_spec('ham') is not None
-                    assert pytestconfig.pluginmanager.rewrite_hook.find_spec('hamster') is None
+                    assert pytestconfig.pluginmanager.rewrite_hook.find_spec(
+                        'ham') is not None
+                    assert pytestconfig.pluginmanager.rewrite_hook.find_spec(
+                        'hamster') is None
             """,
         }
         pytester.makepyfile(**contents)
@@ -687,9 +710,13 @@ def test_dict_wrap(self) -> None:
         ]
 
         long_a = "a" * 80
-        sub = {"long_a": long_a, "sub1": {"long_a": "substring that gets wrapped " * 3}}
+        sub = {
+            "long_a": long_a,
+            "sub1": {"long_a": "substring that gets wrapped " * 3},
+        }
         d1 = {"env": {"sub": sub}}
         d2 = {"env": {"sub": sub}, "new": 1}
+
         diff = callequal(d1, d2, verbose=True)
         assert diff == [
             "{'env': {'sub... wrapped '}}}} == {'env': {'sub...}}}, 'new': 1}",
@@ -702,14 +729,13 @@ def test_dict_wrap(self) -> None:
             "  {",
             "      'env': {",
             "          'sub': {",
-            f"              'long_a': '{long_a}',",
+            f"              'long_a': {long_a!r},",
             "              'sub1': {",
             "                  'long_a': 'substring that gets wrapped substring that gets wrapped '",
             "                  'substring that gets wrapped ',",
             "              },",
             "          },",
             "      },",
-            "-     'new': 1,",
             "  }",
         ]
 

testing/test_collection.py

@@ -408,7 +408,8 @@ def __init__(self, path):
                 def __fspath__(self):
                     return "path"
 
-            collect_ignore = [MyPathLike('hello'), 'test_world.py', Path('bye')]
+            collect_ignore = [MyPathLike(
+                'hello'), 'test_world.py', Path('bye')]
 
             def pytest_addoption(parser):
                 parser.addoption("--XX", action="store_true", default=False)
@@ -768,9 +769,13 @@ def testmethod_two(self, arg0):
 
         # let's also test getmodpath here
         assert items[0].getmodpath() == "testone"  # type: ignore[attr-defined]
+
         assert items[1].getmodpath() == "TestX.testmethod_one"  # type: ignore[attr-defined]
+
         assert items[2].getmodpath() == "TestY.testmethod_one"  # type: ignore[attr-defined]
+
         # PR #6202: Fix incorrect result of getmodpath method. (Resolves issue #6189)
+
         assert items[3].getmodpath() == "TestY.testmethod_two[.[]"  # type: ignore[attr-defined]
 
         s = items[0].getmodpath(stopatmodule=False)  # type: ignore[attr-defined]