diff --git a/tests/unittest/test_fix_json_escape_char.py b/tests/unittest/test_fix_json_escape_char.py
new file mode 100644
index 00000000..afc870a2
--- /dev/null
+++ b/tests/unittest/test_fix_json_escape_char.py
@@ -0,0 +1,21 @@
+from pr_agent.algo.utils import fix_json_escape_char
+
+
+class TestFixJsonEscapeChar:
+    def test_valid_json(self):
+        """Return unchanged when input JSON is already valid"""
+        text = '{"a": 1, "b": "ok"}'
+        expected_output = {"a": 1, "b": "ok"}
+        assert fix_json_escape_char(text) == expected_output
+
+    def test_single_control_char(self):
+        """Remove a single ASCII control-character"""
+        text = '{"msg": "hel\x01lo"}'
+        expected_output = {"msg": "hel lo"}
+        assert fix_json_escape_char(text) == expected_output
+
+    def test_multiple_control_chars(self):
+        """Remove multiple control-characters recursively"""
+        text = '{"x": "A\x02B\x03C"}'
+        expected_output = {"x": "A B C"}
+        assert fix_json_escape_char(text) == expected_output