Set an attribute to test methods.

@overload attribute(name, value)

  @example
    attribute :speed, :slow
    def test_my_slow_method
      self[:speed] # => :slow
    end

  @param [Object] name the attribute name
  @param [Object] value the attribute value
  @return [void]

@overload attribute(name, value, *method_names)

  @example
    def test_my_slow_method1
      self[:speed] # => :slow
    end

    attribute :speed, :slow, :test_my_slow_method1, :test_my_slow_method2

    def test_my_slow_method2
      self[:speed] # => :slow
    end

  @param [Object] name the attribute name
  @param [Object] value the attribute value
  @param [Array<Symbol, String>] method_names the test method names set the attribute
  @return [void]

@overload attribute(name, value, options)

  @example
    attribute :speed, :slow, keep: true
    def test_my_slow_method1
      self[:speed] # => :slow
    end

    def test_my_slow_method2
      self[:speed] # => :slow
    end

  @param [Object] name the attribute name
  @param [Object] value the attribute value
  @option options [Boolean] :keep whether or not to set attribute to following test methods
  @return [void]

@overload attribute(name, value, options, *method_names)

  @example
    def test_my_slow_method1
      self[:speed] # => :slow
    end

    # There are no valid options for now.
    attribute :speed, :slow, {}, :test_my_slow_method1

    def test_my_slow_method2
      self[:speed] # => nil
    end

  @param [Object] name the attribute name
  @param [Object] value the attribute value
  @param [Hash] options ignored
  @param [Array<Symbol, String>] method_names the test method names set the attribute
  @return [void]