From b86ab0763297cbde2ff0d986570bd923f5e195af Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Mon, 6 Apr 2026 18:38:42 -1000
Subject: [PATCH] [core] Fix test for byte-length error message, add ByteLength
 and multibyte tests

---
 tests/unit_tests/test_config_validation.py | 44 ++++++++++++++++++----
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/tests/unit_tests/test_config_validation.py b/tests/unit_tests/test_config_validation.py
index c1849daf4b..ce941b40dc 100644
--- a/tests/unit_tests/test_config_validation.py
+++ b/tests/unit_tests/test_config_validation.py
@@ -149,17 +149,36 @@ def test_icon__invalid():
 
 
 def test_icon__max_length():
-    """Test that icons exceeding 63 characters are rejected."""
-    # Exactly 63 chars should pass
-    max_icon = "mdi:" + "a" * 59  # 63 chars total
+    """Test that icons exceeding 63 bytes are rejected."""
+    # Exactly 63 bytes should pass
+    max_icon = "mdi:" + "a" * 59  # 63 bytes total
     assert config_validation.icon(max_icon) == max_icon
 
-    # 64 chars should fail
-    too_long = "mdi:" + "a" * 60  # 64 chars total
+    # 64 bytes should fail
+    too_long = "mdi:" + "a" * 60  # 64 bytes total
     with pytest.raises(Invalid, match="Icon string is too long"):
         config_validation.icon(too_long)
 
 
+def test_byte_length() -> None:
+    """Test ByteLength validator checks UTF-8 byte length, not char count."""
+    validator = config_validation.ByteLength(max=10)  # pylint: disable=no-member
+
+    # ASCII: 10 chars = 10 bytes, should pass
+    assert validator("a" * 10) == "a" * 10
+
+    # ASCII: 11 chars = 11 bytes, should fail
+    with pytest.raises(Invalid, match="too long.*11 bytes.*max 10"):
+        validator("a" * 11)
+
+    # Multibyte: 3 chars × 3 bytes = 9 bytes, should pass
+    assert validator("温度传") == "温度传"
+
+    # Multibyte: 4 chars × 3 bytes = 12 bytes, should fail
+    with pytest.raises(Invalid, match="too long.*12 bytes.*max 10"):
+        validator("温度传感")
+
+
 @pytest.mark.parametrize("value", ("True", "YES", "on", "enAblE", True))
 def test_boolean__valid_true(value):
     assert config_validation.boolean(value) is True
@@ -567,14 +586,23 @@ def test_validate_entity_name__slash_replaced_with_warning(
 
 
 def test_validate_entity_name__max_length() -> None:
-    # 120 chars should pass
+    # 120 bytes should pass
     assert config_validation._validate_entity_name("x" * 120) == "x" * 120
 
-    # 121 chars should fail
-    with pytest.raises(Invalid, match="too long.*121 chars.*Maximum.*120"):
+    # 121 bytes should fail
+    with pytest.raises(Invalid, match="too long.*121 bytes.*Maximum.*120"):
         config_validation._validate_entity_name("x" * 121)
 
 
+def test_validate_entity_name__multibyte_byte_length() -> None:
+    # 40 chars of 3-byte UTF-8 = 120 bytes, should pass
+    assert config_validation._validate_entity_name("温" * 40) == "温" * 40
+
+    # 41 chars of 3-byte UTF-8 = 123 bytes, should fail (over 120 byte limit)
+    with pytest.raises(Invalid, match="too long.*123 bytes.*Maximum.*120"):
+        config_validation._validate_entity_name("温" * 41)
+
+
 def test_validate_entity_name__none_without_friendly_name() -> None:
     # When name is "None" and friendly_name is not set, it should fail
     CORE.friendly_name = None