From 9aa2fa5aec295998db4a67d2927db4c631e8b845 Mon Sep 17 00:00:00 2001
From: JingHao-Leon <102573344+JingHao-Leon@users.noreply.github.com>
Date: Mon, 19 Oct 2026 18:21:00 +0800
Subject: [PATCH] Validate asyncio marker loop_scope via _validate_scope

The marker's loop_scope was checked with a bare assert, so an invalid value
surfaced as AssertionError: assert 'x' in {'class', 'function', ...}. Use the
helper that already validates the two ini options instead, so the reported
message names the argument and lists the valid scopes.
---
 changelog.d/1584.fixed.rst        |  1 +
 pytest_asyncio/plugin.py          |  3 +--
 tests/test_fixture_loop_scopes.py | 20 ++++++++++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 changelog.d/1584.fixed.rst

diff --git a/changelog.d/1584.fixed.rst b/changelog.d/1584.fixed.rst
new file mode 100644
index 00000000..1e146fc3
--- /dev/null
+++ b/changelog.d/1584.fixed.rst
@@ -0,0 +1 @@
+Fixed an invalid ``loop_scope`` in the ``asyncio`` marker being reported as a bare ``AssertionError`` exposing a Python set repr, instead of a usage error that names the argument and lists the valid scopes.
diff --git a/pytest_asyncio/plugin.py b/pytest_asyncio/plugin.py
index 38b75e41..e99a8d03 100644
--- a/pytest_asyncio/plugin.py
+++ b/pytest_asyncio/plugin.py
@@ -979,8 +979,7 @@ def _parse_asyncio_marker(
     scope = asyncio_marker.kwargs.get("loop_scope") or asyncio_marker.kwargs.get(
         "scope"
     )
-    if scope is not None:
-        assert scope in {"function", "class", "module", "package", "session"}
+    _validate_scope(scope, "loop_scope")
     marker_value = asyncio_marker.kwargs.get("loop_factories")
     if marker_value is None:
         return scope, None
diff --git a/tests/test_fixture_loop_scopes.py b/tests/test_fixture_loop_scopes.py
index a25e56a0..a051b8a1 100644
--- a/tests/test_fixture_loop_scopes.py
+++ b/tests/test_fixture_loop_scopes.py
@@ -126,3 +126,23 @@ def test_invalid_default_fixture_loop_scope_raises_error(pytester: Pytester):
             "function, class, module, package, session."
         ]
     )
+
+
+def test_invalid_marker_loop_scope_raises_error(pytester: Pytester):
+    pytester.makeini("[pytest]\nasyncio_default_fixture_loop_scope = function")
+    pytester.makepyfile("""\
+        import pytest
+
+        @pytest.mark.asyncio(loop_scope="invalid_scope")
+        async def test_invalid_loop_scope():
+            pass
+        """)
+    result = pytester.runpytest("--assert=plain")
+    # The exception class is rendered as pytest.UsageError on newer pytest and as
+    # _pytest.config.exceptions.UsageError on the oldest supported version.
+    result.stdout.fnmatch_lines(
+        [
+            "*UsageError: 'invalid_scope' is not a valid loop_scope. "
+            "Valid scopes are: function, class, module, package, session."
+        ]
+    )