diff --git a/utils.py b/utils.py
index 63d7c2a..cdafe2d 100644
--- a/utils.py
+++ b/utils.py
@@ -1,12 +1,11 @@
 import re
 
-_CLASS_FINDER = re.compile(r'^\s*class\s+([A-Z][a-zA-Z0-9_]*)(?:\s*\([^)]*\))?\s*:')
+_CLASS_FINDER = re.compile(r'^\s*class\s+([A-Z][a-zA-Z0-9_]*)(?:\s|\(|:)', re.MULTILINE)
 
 
 def guess_classname(code: str) -> str:
-    for line in code.splitlines():
-        if match := _CLASS_FINDER.search(line):
-            return match.group(1)
+    if match := _CLASS_FINDER.search(code):
+        return match.group(1)
     raise ValueError('Cannot find classname in code. Expected a class definition like `class ClassName:`')
 
 
diff --git a/utils_test.py b/utils_test.py
index 9d88536..ee9cbd5 100644
--- a/utils_test.py
+++ b/utils_test.py
@@ -81,3 +81,53 @@ def test_camel_to_snake_mixed_case(self):
     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")
+
+    def test_camel_to_snake_trailing_capital(self):
+        self.assertEqual(camel_to_snake("MyClassA"), "my_class_a")
+
+    def test_camel_to_snake_all_caps(self):
+        self.assertEqual(camel_to_snake("HTTP"), "http")
+        self.assertEqual(camel_to_snake("HTTPServer"), "http_server")
+
+    def test_guess_classname_indented(self):
+        code = "    class IndentedClass:\n        pass"
+        self.assertEqual(guess_classname(code), "IndentedClass")
+
+    def test_guess_classname_with_multiline_docstring_before(self):
+        code = '"""\nThis is a docstring\n"""\nclass MyClass:\n    pass'
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_guess_classname_multiline_definition(self):
+        # Test that it works with multiline class definitions
+        code = "class MyClass(\n    Base\n):\n    pass"
+        self.assertEqual(guess_classname(code), "MyClass")
+
+    def test_camel_to_snake_with_middle_acronym(self):
+        self.assertEqual(camel_to_snake("APIRequestResponse"), "api_request_response")
+
+    def test_camel_to_snake_with_numbers_and_acronyms(self):
+        self.assertEqual(camel_to_snake("HTML5Parser"), "html5_parser")
+        self.assertEqual(camel_to_snake("JSON2HTML"), "json2_html")
+
+    def test_camel_to_snake_starting_with_number(self):
+        self.assertEqual(camel_to_snake("123ClassName"), "123_class_name")
+
+    def test_camel_to_snake_already_snake_with_numbers(self):
+        self.assertEqual(camel_to_snake("already_snake_123"), "already_snake_123")
+
+    def test_camel_to_snake_with_special_characters(self):
+        # camel_to_snake doesn't explicitly handle dashes, but let's see what it does
+        self.assertEqual(camel_to_snake("StringWith-Dash"), "string_with-dash")
+
+    def test_guess_classname_with_underscore(self):
+        code = "class My_Class: pass"
+        self.assertEqual(guess_classname(code), "My_Class")
+
+    def test_guess_classname_not_at_start_of_line(self):
+        code = "# class NotMe:\nclass Me: pass"
+        self.assertEqual(guess_classname(code), "Me")
+
+    def test_guess_classname_commented_out(self):
+        code = "# class NotMe: pass"
+        with self.assertRaises(ValueError):
+            guess_classname(code)