diff --git a/utils.py b/utils.py
index 19748af..63d7c2a 100644
--- a/utils.py
+++ b/utils.py
@@ -1,16 +1,15 @@
 import re
 
-_CLASS_FINDER = re.compile(r'^\s*class\s+([A-Z][a-zA-Z0-9_]*)\s*\((?:ABC|object)\)\s*:\s*')
+_CLASS_FINDER = re.compile(r'^\s*class\s+([A-Z][a-zA-Z0-9_]*)(?:\s*\([^)]*\))?\s*:')
 
 
 def guess_classname(code: str) -> str:
     for line in code.splitlines():
         if match := _CLASS_FINDER.search(line):
             return match.group(1)
-    raise ValueError('Cannot find classname in code. Expected a class definition like `class ClassName(ABC):`')
+    raise ValueError('Cannot find classname in code. Expected a class definition like `class ClassName:`')
 
 
 def camel_to_snake(input: str) -> str:
     s1 = re.sub(r'(?<=[a-z])(?=[A-Z])|(?<=[A-Z])(?=[A-Z][a-z])', '_', input)
-    s2 = re.sub(r'([a-zA-Z])([0-9])', r'\1\2', s1)
-    return re.sub(r'([0-9])([A-Z])', r'\1_\2', s2).lower()
+    return re.sub(r'([0-9])([A-Z])', r'\1_\2', s1).lower()
diff --git a/utils_test.py b/utils_test.py
index a040080..9d88536 100644
--- a/utils_test.py
+++ b/utils_test.py
@@ -27,8 +27,7 @@ def test_guess_classname_with_multiple_classes(self):
 
     def test_guess_classname_with_complex_class_definition(self):
         code = "class MyComplexClass(object, metaclass=MyMeta): pass"
-        with self.assertRaises(ValueError):
-            guess_classname(code)
+        self.assertEqual(guess_classname(code), "MyComplexClass")
 
     def test_camel_to_snake_edge_case(self):
         self.assertEqual(camel_to_snake(""), "")
@@ -52,3 +51,33 @@ def test_camel_to_snake_with_numbers(self):
     def test_camel_to_snake_single_word(self):
         self.assertEqual(camel_to_snake("hello"), "hello")
         self.assertEqual(camel_to_snake("WORLD"), "world")
+
+    def test_guess_classname_no_parentheses(self):
+        code = "class MyClass: pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_guess_classname_other_parent(self):
+        code = "class MyClass(Base): pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_guess_classname_multiple_parents(self):
+        code = "class MyClass(Base1, Base2): pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_guess_classname_with_comment(self):
+        code = "class MyClass(ABC): # This is a class\n    pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_guess_classname_after_comments(self):
+        code = "# Comment\n\nclass MyClass(ABC): pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_camel_to_snake_already_snake(self):
+        self.assertEqual(camel_to_snake("already_snake_case"), "already_snake_case")
+
+    def test_camel_to_snake_mixed_case(self):
+        self.assertEqual(camel_to_snake("My_Mixed_Case"), "my_mixed_case")
+
+    def test_camel_to_snake_complex_numbers(self):
+        self.assertEqual(camel_to_snake("A1B2C3"), "a1_b2_c3")
+        self.assertEqual(camel_to_snake("v6Address"), "v6_address")