text: import unittest
  
  from circular_buffer import (
      CircularBuffer,
      BufferEmptyException,
      BufferFullException,
  )
  
  # Tests adapted from `problem-specifications//canonical-data.json`
  
  
  class CircularBufferTest(unittest.TestCase):
      def test_reading_empty_buffer_should_fail(self):
          buf = CircularBuffer(1)
          with self.assertRaises(BufferError) as err:
              buf.read()
  
          self.assertEqual(type(err.exception), BufferEmptyException)
          self.assertEqual(err.exception.args[0], "Circular buffer is empty")
  
      def test_can_read_an_item_just_written(self):
          buf = CircularBuffer(1)
          buf.write("1")
          self.assertEqual(buf.read(), "1")
  
      def test_each_item_may_only_be_read_once(self):
          buf = CircularBuffer(1)
          buf.write("1")
          self.assertEqual(buf.read(), "1")
          with self.assertRaises(BufferError) as err:
              buf.read()
  
          self.assertEqual(type(err.exception), BufferEmptyException)
          self.assertEqual(err.exception.args[0], "Circular buffer is empty")
  
      def test_items_are_read_in_the_order_they_are_written(self):
          buf = CircularBuffer(2)
          buf.write("1")
          buf.write("2")
          self.assertEqual(buf.read(), "1")
          self.assertEqual(buf.read(), "2")
  
      def test_full_buffer_can_t_be_written_to(self):
          buf = CircularBuffer(1)
          buf.write("1")
          with self.assertRaises(BufferError) as err:
              buf.write("2")
  
          self.assertEqual(type(err.exception), BufferFullException)
          self.assertEqual(err.exception.args[0], "Circular buffer is full")
  
      def test_a_read_frees_up_capacity_for_another_write(self):
          buf = CircularBuffer(1)
          buf.write("1")
          self.assertEqual(buf.read(), "1")
          buf.write("2")
          self.assertEqual(buf.read(), "2")
  
      def test_read_position_is_maintained_even_across_multiple_writes(self):
          buf = CircularBuffer(3)
          buf.write("1")
          buf.write("2")
          self.assertEqual(buf.read(), "1")
          buf.write("3")
          self.assertEqual(buf.read(), "2")
          self.assertEqual(buf.read(), "3")
  
      def test_items_cleared_out_of_buffer_can_t_be_read(self):
          buf = CircularBuffer(1)
          buf.write("1")
          buf.clear()
          with self.assertRaises(BufferError) as err:
              buf.read()
  
          self.assertEqual(type(err.exception), BufferEmptyException)
          self.assertEqual(err.exception.args[0], "Circular buffer is empty")
  
      def test_clear_frees_up_capacity_for_another_write(self):
          buf = CircularBuffer(1)
          buf.write("1")
          buf.clear()
          buf.write("2")
          self.assertEqual(buf.read(), "2")
  
      def test_clear_does_nothing_on_empty_buffer(self):
          buf = CircularBuffer(1)
          buf.clear()
          buf.write("1")
          self.assertEqual(buf.read(), "1")
  
      def test_overwrite_acts_like_write_on_non_full_buffer(self):
          buf = CircularBuffer(2)
          buf.write("1")
          buf.overwrite("2")
          self.assertEqual(buf.read(), "1")
          self.assertEqual(buf.read(), "2")
  
      def test_overwrite_replaces_the_oldest_item_on_full_buffer(self):
          buf = CircularBuffer(2)
          buf.write("1")
          buf.write("2")
          buf.overwrite("3")
          self.assertEqual(buf.read(), "2")
          self.assertEqual(buf.read(), "3")
  
      def test_overwrite_replaces_the_oldest_item_remaining_in_buffer_following_a_read(
          self,
      ):
          buf = CircularBuffer(3)
          buf.write("1")
          buf.write("2")
          buf.write("3")
          self.assertEqual(buf.read(), "1")
          buf.write("4")
          buf.overwrite("5")
          self.assertEqual(buf.read(), "3")
          self.assertEqual(buf.read(), "4")
          self.assertEqual(buf.read(), "5")
  
      def test_initial_clear_does_not_affect_wrapping_around(self):
          buf = CircularBuffer(2)
          buf.clear()
          buf.write("1")
          buf.write("2")
          buf.overwrite("3")
          buf.overwrite("4")
          self.assertEqual(buf.read(), "3")
          self.assertEqual(buf.read(), "4")
          with self.assertRaises(BufferError) as err:
              buf.read()
  
          self.assertEqual(type(err.exception), BufferEmptyException)
          self.assertEqual(err.exception.args[0], "Circular buffer is empty")
  