old_contents: """Tests for the add function"""
  from unittest import TestCase
  
  import adder
  
  class TestAdd(TestCase):
      """Test the add function"""
      def test_int(self):
          """Test adding integers"""
          result = adder.add(3, 4)
          self.assertEqual(result, 7)
  
      def test_float(self):
          """Test adding floats"""
          result = adder.add(3.5, 4.5)
          self.assertEqual(result, 8.0)
  
      def test_string(self):
          """Test adding strings - should append"""
          result = adder.add("toast", "jam")
          self.assertEqual(result, "toastjam")
  
      def test_mixed(self):
          """Test that mixing types causes a TypeError"""
          with self.assertRaises(TypeError):
              adder.add("toast", 3)
  
new_contents: """Tests for the add function"""
  from unittest import TestCase
  
  import adder
  
  class TestAdd(TestCase):
      """Test the add function"""
      def test_int(self):
          """Test adding integers"""
          result = adder.add(3, 4)
          self.assertEqual(result, 7)
  
      def test_float(self):
          """Test adding floats"""
          result = adder.add(3.5, 4.5)
          self.assertEqual(result, 8.0)
  
      def test_string(self):
          """Test adding strings - should append"""
          result = adder.add("toast", "jam")
          self.assertEqual(result, "toastjam")
  
      def test_mixed(self):
          """Test that mixing types causes a TypeError"""
          with self.assertRaises(TypeError):
              adder.add("toast", 3)
  
  class TestSubtract(TestCase):
      """Test the subtract function"""
      def test_sub(self):
          """Test subtracting integers"""
          result = adder.subtract(4,3)
          self.assertEqual(result, 1)
  
subject: Add subtract tests