diff --git a/tests/test_anf.py b/tests/test_anf.py
index 4072e00..9d212df 100644
--- a/tests/test_anf.py
+++ b/tests/test_anf.py
@@ -84,6 +84,12 @@ def test_equivalence_suite():
         "!(X1 OR X2)",
         "(X1 + X2) * (!X1 + X3)",
         "!X1 AND (!X2 OR X3) OR X1 AND X2",
+        "X1 AND X2 OR X1 AND X3",
+        "!(X1 AND X2) OR (X1 OR X2)",
+        "X1 * X1 * X2 * X2",
+        "X1 + !X1 + X2",
+        "(X1 OR X2) AND (X2 OR X3) AND (X3 OR X1)",
+        "!!(X1 AND !X2) OR X3",
     ]
 
     for f in formulas: