Interface Implementation Test

interface_test.rb

require 'rspec/autorun'

class Parent
  def self.descendants
    ObjectSpace.each_object(Class).select { |klass| klass < self }
  end

  def foo
    fail NotImplementedError
  end
end

class ChildFoo < Parent
  def foo
    'ha'
  end
end

class ChildBar < Parent
  def foo
    'bar'
  end
end

RSpec.describe Parent do
  described_class.descendants.each do |child|
    context child.name do
      it 'implements #foo' do
        expect { child.new.foo }.not_to raise_error
      end
    end
  end
end