ruby - circular-buffer
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ruby/circular-buffer/README.md
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ruby/circular-buffer/README.md
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# Circular Buffer
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A circular buffer, cyclic buffer or ring buffer is a data structure that
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uses a single, fixed-size buffer as if it were connected end-to-end.
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A circular buffer first starts empty and of some predefined length. For
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example, this is a 7-element buffer:
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[ ][ ][ ][ ][ ][ ][ ]
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Assume that a 1 is written into the middle of the buffer (exact starting
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location does not matter in a circular buffer):
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[ ][ ][ ][1][ ][ ][ ]
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Then assume that two more elements are added — 2 & 3 — which get
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appended after the 1:
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[ ][ ][ ][1][2][3][ ]
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If two elements are then removed from the buffer, the oldest values
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inside the buffer are removed. The two elements removed, in this case,
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are 1 & 2, leaving the buffer with just a 3:
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[ ][ ][ ][ ][ ][3][ ]
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If the buffer has 7 elements then it is completely full:
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[6][7][8][9][3][4][5]
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When the buffer is full an error will be raised, alerting the client
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that further writes are blocked until a slot becomes free.
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When the buffer is full, the client can opt to overwrite the oldest
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data with a forced write. In this case, two more elements — A & B —
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are added and they overwrite the 3 & 4:
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[6][7][8][9][A][B][5]
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3 & 4 have been replaced by A & B making 5 now the oldest data in the
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buffer. Finally, if two elements are removed then what would be
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returned is 5 & 6 yielding the buffer:
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[ ][7][8][9][A][B][ ]
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Because there is space available, if the client again uses overwrite
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to store C & D then the space where 5 & 6 were stored previously will
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be used not the location of 7 & 8. 7 is still the oldest element and
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the buffer is once again full.
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[D][7][8][9][A][B][C]
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* * * *
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For installation and learning resources, refer to the
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[Ruby resources page](http://exercism.io/languages/ruby/resources).
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For running the tests provided, you will need the Minitest gem. Open a
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terminal window and run the following command to install minitest:
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gem install minitest
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If you would like color output, you can `require 'minitest/pride'` in
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the test file, or note the alternative instruction, below, for running
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the test file.
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Run the tests from the exercise directory using the following command:
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ruby circular_buffer_test.rb
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To include color from the command line:
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ruby -r minitest/pride circular_buffer_test.rb
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## Source
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Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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ruby/circular-buffer/circular_buffer.rb
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ruby/circular-buffer/circular_buffer.rb
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# Class CircularBuffer
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class CircularBuffer
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class BufferEmptyException < RuntimeError
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end
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class BufferFullException < RuntimeError
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end
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def initialize(buffer_size)
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@buffer = Array.new(buffer_size)
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end
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def read
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raise BufferEmptyException if @front.nil?
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value = @buffer[@front]
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@buffer[@front] = nil
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if @front == @back
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@back = @front = nil
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else
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@front = next_index(@front)
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end
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value
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end
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def write(data, force = false)
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raise BufferFullException if @buffer[next_index(@back)] && !force
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@back = next_index(@back)
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@front = 0 if @front.nil?
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@buffer[@back] = data
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end
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def write!(data)
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@front = next_index(@front) if @buffer[next_index(@front)]
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write(data, true)
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end
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def clear
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@buffer = Array.new(@buffer.size)
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@front = @back = nil
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end
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private
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def next_index(index)
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return 0 if index.nil?
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(index + 1) % @buffer.size
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end
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end
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ruby/circular-buffer/circular_buffer_test.rb
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ruby/circular-buffer/circular_buffer_test.rb
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require 'minitest/autorun'
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require_relative 'circular_buffer'
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class CircularBufferTest < Minitest::Test
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def test_read_empty_buffer_throws_buffer_empty_exception
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buffer = CircularBuffer.new(1)
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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def test_write_and_read_back_one_item
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# skip
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buffer = CircularBuffer.new(1)
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buffer.write '1'
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assert_equal '1', buffer.read
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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def test_write_and_read_back_multiple_items
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# skip
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buffer = CircularBuffer.new(2)
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buffer.write '1'
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buffer.write '2'
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assert_equal '1', buffer.read
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assert_equal '2', buffer.read
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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def test_clearing_buffer
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# skip
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buffer = CircularBuffer.new(3)
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('1'..'3').each { |i| buffer.write i }
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buffer.clear
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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buffer.write '1'
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buffer.write '2'
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assert_equal '1', buffer.read
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buffer.write '3'
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assert_equal '2', buffer.read
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end
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def test_alternate_write_and_read
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# skip
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buffer = CircularBuffer.new(2)
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buffer.write '1'
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assert_equal '1', buffer.read
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buffer.write '2'
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assert_equal '2', buffer.read
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end
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def test_reads_back_oldest_item
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# skip
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buffer = CircularBuffer.new(3)
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buffer.write '1'
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buffer.write '2'
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buffer.read
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buffer.write '3'
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assert_equal '2', buffer.read
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assert_equal '3', buffer.read
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end
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def test_writing_to_a_full_buffer_throws_an_exception
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# skip
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buffer = CircularBuffer.new(2)
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buffer.write '1'
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buffer.write '2'
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assert_raises(CircularBuffer::BufferFullException) { buffer.write 'A' }
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end
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def test_overwriting_oldest_item_in_a_full_buffer
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# skip
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buffer = CircularBuffer.new(2)
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buffer.write '1'
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buffer.write '2'
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buffer.write! 'A'
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assert_equal '2', buffer.read
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assert_equal 'A', buffer.read
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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def test_forced_writes_to_non_full_buffer_should_behave_like_writes
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# skip
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buffer = CircularBuffer.new(2)
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buffer.write '1'
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buffer.write! '2'
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assert_equal '1', buffer.read
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assert_equal '2', buffer.read
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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def test_alternate_read_and_write_into_buffer_overflow
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# skip
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buffer = CircularBuffer.new(5)
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('1'..'3').each { |i| buffer.write i }
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buffer.read
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buffer.read
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buffer.write '4'
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buffer.read
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('5'..'8').each { |i| buffer.write i }
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buffer.write! 'A'
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buffer.write! 'B'
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('6'..'8').each do |i|
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assert_equal i, buffer.read
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end
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assert_equal 'A', buffer.read
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assert_equal 'B', buffer.read
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assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
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end
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end
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