eigenclass_modification_spec.rb

describe 'simple object' do

  class A
    def initialize
      @c = 'ccc'
      @d = 'ddd'
    end

    def default
      'aaa'
    end
  end

  module B
    def self.extended(base)
      base.class.send(:define_method, :c) do
        @c
      end

      class << base
        define_method(:d) do
          @d
        end
      end
    end

    def default
      'bbb'
    end
  end

  a = A.new
  b = A.new
  c = A.new

  describe 'a' do
    it 'has the original default' do
      expect(a.default).to eq 'aaa'
    end

    it 'does not have the extended methods' do
      expect { a.c }.to raise_error Exception
      expect { a.d }.to raise_error Exception
    end
  end

  describe 'a' do
    it 'has the updated default' do
      b.extend B
      expect(b.default).to eq 'bbb'
    end

    it 'has the extended methods' do
      expect(b.c).to eq 'ccc'
      expect(b.d).to eq 'ddd'
    end
  end

  describe 'a' do
    it 'has the original default' do
      expect(c.default).to eq 'aaa'
    end

    it 'has the extended c method' do
      expect(c.c).to eq 'ccc'
    end

    it 'does not have the extended d method' do
      expect{ c.d }.to raise_error Exception
    end
  end
end