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to Diamond in the Ruby Track

Published at Mar 10 2019 · 0 comments
Test suite

The diamond kata takes as its input a letter, and outputs it in a diamond shape. Given a letter, it prints a diamond starting with 'A', with the supplied letter at the widest point.


  • The first row contains one 'A'.
  • The last row contains one 'A'.
  • All rows, except the first and last, have exactly two identical letters.
  • All rows have as many trailing spaces as leading spaces. (This might be 0).
  • The diamond is horizontally symmetric.
  • The diamond is vertically symmetric.
  • The diamond has a square shape (width equals height).
  • The letters form a diamond shape.
  • The top half has the letters in ascending order.
  • The bottom half has the letters in descending order.
  • The four corners (containing the spaces) are triangles.


In the following examples, spaces are indicated by · characters.

Diamond for letter 'A':


Diamond for letter 'C':


Diamond for letter 'E':


For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby diamond_test.rb

To include color from the command line:

ruby -r minitest/pride diamond_test.rb


Seb Rose http://claysnow.co.uk/recycling-tests-in-tdd/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


require 'minitest/autorun'
require_relative 'diamond'

class DiamondTest < Minitest::Test
  def test_letter_a
    answer = Diamond.make_diamond('A')
    assert_equal "A\n", answer

  def test_letter_c
    answer = Diamond.make_diamond('C')
    string = "  A  \n"\
             " B B \n"\
             "C   C\n"\
             " B B \n"\
             "  A  \n"
    assert_equal string, answer

  def test_letter_e
    answer = Diamond.make_diamond('E')
    string = "    A    \n"\
             "   B B   \n"\
             "  C   C  \n"\
             " D     D \n"\
             "E       E\n"\
             " D     D \n"\
             "  C   C  \n"\
             "   B B   \n"\
             "    A    \n"
    assert_equal string, answer
require 'byebug'

class Diamond
  def self.make_diamond(to)
    r = ('A'..to).to_a
    width = r.length
    top = []
    bottom = []

    r.each_with_index do |l, i|
      half = l.rjust(i + 1).ljust(width)
      line = "#{ half.reverse }#{ half[1..-1] }"

    lines = top + bottom[1..-1]


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