From abda8ff1c8070f1a9320740f3761faa5898f2f5e Mon Sep 17 00:00:00 2001
From: Stainless Bot <dev@stainlessapi.com>
Date: Thu, 25 Apr 2024 03:38:21 +0000
Subject: [PATCH] chore(internal): update test helper function

---
 tests/utils.py | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tests/utils.py b/tests/utils.py
index 43c3cb5cfe..060b99339f 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -97,7 +97,22 @@ def assert_matches_type(
             assert_matches_type(key_type, key, path=[*path, "<dict key>"])
             assert_matches_type(items_type, item, path=[*path, "<dict item>"])
     elif is_union_type(type_):
-        for i, variant in enumerate(get_args(type_)):
+        variants = get_args(type_)
+
+        try:
+            none_index = variants.index(type(None))
+        except ValueError:
+            pass
+        else:
+            # special case Optional[T] for better error messages
+            if len(variants) == 2:
+                if value is None:
+                    # valid
+                    return
+
+                return assert_matches_type(type_=variants[not none_index], value=value, path=path)
+
+        for i, variant in enumerate(variants):
             try:
                 assert_matches_type(variant, value, path=[*path, f"variant {i}"])
                 return