Fix isset() to cover dict.items() and dict.keys() in set comparisons

AUTHORS

@@ -80,6 +80,7 @@ Brian Okken
 Brianna Laugher
 Bruno Oliveira
 Cal Jacobson
+croc100
 Cal Leeming
 Carl Friedrich Bolz
 Carlos Jenkins

changelog/12860.improvement.rst

@@ -0,0 +1 @@
+Assertion diffs for ``dict.items()`` and ``dict.keys()`` comparisons (``>=``, ``<=``, ``>``, ``<``, ``==``) now show which items are missing, the same way set comparisons do.

src/_pytest/assertion/_guards.py

@@ -2,6 +2,7 @@
 
 import collections.abc
 from collections.abc import Mapping
+from collections.abc import Set as AbstractSet
 import dataclasses
 from typing import TypeGuard
 
@@ -18,8 +19,8 @@ def ismapping(x: object) -> TypeGuard[Mapping[object, object]]:
     return isinstance(x, Mapping)
 
 
-def isset(x: object) -> TypeGuard[set[object] | frozenset[object]]:
-    return isinstance(x, set | frozenset)
+def isset(x: object) -> TypeGuard[AbstractSet[object]]:
+    return isinstance(x, AbstractSet)
 
 
 def isnamedtuple(obj: object) -> bool:

testing/test_assertion.py

@@ -1870,6 +1870,38 @@ def test_hello():
             ]
         )
 
+    @pytest.mark.parametrize("op", [">=", "<="])
+    def test_dict_items_view_subset(self, op, pytester: Pytester) -> None:
+        """dict.items() supports set-like comparisons; assert diff should show the missing items."""
+        if op == ">=":
+            pytester.makepyfile(
+                """
+                def test_hello():
+                    x = {"a": 1, "b": 2}
+                    y = {"a": 1, "b": 2, "c": 3}
+                    assert x.items() >= y.items()
+            """
+            )
+        else:
+            pytester.makepyfile(
+                """
+                def test_hello():
+                    x = {"a": 1, "b": 2, "c": 3}
+                    y = {"a": 1, "b": 2}
+                    assert x.items() <= y.items()
+            """
+            )
+        result = pytester.runpytest()
+        side = "right" if op == ">=" else "left"
+        result.stdout.fnmatch_lines(
+            [
+                "*def test_hello():*",
+                f"*assert x.items() {op} y.items()*",
+                f"*E*Extra items in the {side} set:*",
+                "*E*('c', 3)*",
+            ]
+        )
+
 
 def test_assertrepr_loaded_per_dir(pytester: Pytester) -> None:
     pytester.makepyfile(test_base=["def test_base(): assert 1 == 2"])