Preserve dict insertion order in safeformat output (fixes #13503)

changelog/13503.bugfix.rst

@@ -0,0 +1 @@
+Fixes dict output in assertion failures to preserve insertion order. (#13503)

src/_pytest/_io/saferepr.py

@@ -87,7 +87,7 @@ def safeformat(obj: object) -> str:
     with a short exception info.
     """
     try:
-        return pprint.pformat(obj)
+        return pprint.pformat(obj, sort_dicts=False)
     except Exception as exc:
         return _format_repr_exception(exc, obj)
 

testing/io/test_saferepr.py

@@ -192,3 +192,15 @@ def __repr__(self):
     assert saferepr_unlimited(A()).startswith(
         "<[ValueError(42) raised in repr()] A object at 0x"
     )
+
+
+def test_saferepr_dict_insertion_order():
+    from _pytest._io.saferepr import safeformat
+
+    d = {}
+    d["z"] = 1
+    d["a"] = 2
+    d["m"] = 3
+    output = safeformat(d)
+    # output should contain 'z', 'a', 'm' in this order (not 'a', 'm', 'z')
+    assert output.find("'z'") < output.find("'a'") < output.find("'m'")