diff --git a/tests/test_utils_trinary.py b/tests/test_utils_trinary.py
new file mode 100644
index 00000000..f91fe6b7
--- /dev/null
+++ b/tests/test_utils_trinary.py
@@ -0,0 +1,34 @@
+import pytest
+import sys
+import os
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+from slic.utils.trinary import *
+
+def test_check_trinary_valid_values():
+    # These calls should not raise any exception and return None
+    assert check_trinary(True) is None
+    assert check_trinary(False) is None
+    assert check_trinary(None) is None
+
+def test_check_trinary_invalid_value():
+    # These values are not allowed and should raise ValueError
+    with pytest.raises(ValueError, match=r"Trinary .+ not in"):
+        check_trinary("yes")
+
+    with pytest.raises(ValueError):
+        check_trinary(0)
+
+    with pytest.raises(ValueError):
+        check_trinary(1)
+
+    with pytest.raises(ValueError):
+        check_trinary([])
+
+def test_check_trinary_with_custom_allowed_values():
+    # Valid custom values should pass without error
+    assert check_trinary("maybe", allowed_values=("yes", "no", "maybe")) is None
+    assert check_trinary("yes", allowed_values=("yes", "no", "maybe")) is None
+
+    # Invalid custom value should raise ValueError
+    with pytest.raises(ValueError):
+        check_trinary("never", allowed_values=("yes", "no", "maybe"))