Remove Mutant.singleton_subclass_instance

* Only one call side, implementation was inlined

lib/mutant.rb

@@ -37,33 +37,6 @@ module Mutant
   def self.ci?
     ENV.key?('CI')
   end
-
-  # Define instance of subclassed superclass as constant
-  #
-  # @param [Class] superclass
-  # @param [Symbol] name
-  #
-  # @return [self]
-  #
-  # @api private
-  #
-  # rubocop:disable MethodLength
-  #
-  def self.singleton_subclass_instance(name, superclass, &block)
-    klass = Class.new(superclass) do
-      def inspect
-        self.class.name
-      end
-
-      define_singleton_method(:name) do
-        "#{superclass.name}::#{name}".freeze
-      end
-    end
-    klass.class_eval(&block)
-    superclass.const_set(name, klass.new)
-    self
-  end
-
 end # Mutant
 
 require 'mutant/version'

lib/mutant/color.rb

@@ -15,7 +15,7 @@ module Mutant
       "\e[#{@code}m#{text}\e[0m"
     end
 
-    Mutant.singleton_subclass_instance('NONE', self) do
+    NONE = Class.new(self) do
 
       # Format null color
       #
@@ -41,7 +41,7 @@ module Mutant
       def initialize
       end
 
-    end
+    end.new
 
     RED   = Color.new(31)
     GREEN = Color.new(32)

spec/unit/mutant_spec.rb

@@ -12,38 +12,4 @@ RSpec.describe Mutant do
 
     it { should be(result) }
   end
-
-  describe '.singleton_subclass_instance' do
-    subject { object.singleton_subclass_instance(name, superclass, &block) }
-
-    before { subject }
-
-    let(:name)       { 'Test'                }
-    let(:block)      { proc { def foo; end } }
-    let(:superclass) { Class.new             }
-
-    let(:generated) { superclass.const_get(:Test) }
-
-    it_should_behave_like 'a command method'
-
-    it 'sets expected name' do
-      name = generated.class.name
-      expect(name).to eql("::#{self.name}")
-      expect(name).to be_frozen
-    end
-
-    it 'stores instance of subclass' do
-      expect(generated).to be_kind_of(superclass)
-    end
-
-    it 'evaluates the context of proc inside subclass' do
-      expect(generated).to respond_to(:foo)
-    end
-
-    it 'generates nice #inspect' do
-      inspect = generated.inspect
-      expect(inspect).to eql("::#{self.name}")
-      expect(inspect).to be_frozen
-    end
-  end
 end