class RSpec::Mocks::ConstantMutator::UndefinedConstantSetter

def mutate
  @parent = @context_parts.inject(Object) do |klass, name|
    if const_defined_on?(klass, name)
      get_const_defined_on(klass, name)
    else
      ConstantMutator.stub(name_for(klass, name), Module.new)
    end
  end
  @parent.const_set(@const_name, @mutated_value)
end