Rspec

Custom matchers#constant_defined

module CustomMatchers

  def define_constant(expected)
    DefineConstant.new(expected)
  end

  class DefineConstant
    def initialize(expected_constant)
      @expected_constant = expected_constant
    end

    def matches?(actual_object)
      @actual_object = actual_object.is_a?(Class) ? actual_object : actual_object.class
      constant_defined? && value_matches?  
    end
    
    # default value for the constant
    def with_value(value)
      @value = value
      self
    end
    
    def failure_message
      "expected " + error_messages
    end
    
    def negative_failure_message
      "did not expect " + error_messages
    end
    
    def description
      [].tap do |array|
        array << "define constant #{@expected_constant}"
        array << "with value of #{@value}" if instance_variable_defined?("@value") && value_matches?
      end.join(" ")
    end
    
    private
    
    def constant_defined?
      @actual_object.const_defined?(@expected_constant.to_sym)
    end 
    
    def value_matches?
      instance_variable_defined?("@value") ? @actual_object.const_get(@expected_constant.to_sym) == @value : true
    end
    
    def error_messages
      [].tap do |array|
        array << "#{@actual_object} to define constant #{@expected_constant.to_sym}" unless constant_defined?
        array << "#{@expected_constant.to_sym} to have value #{@value}" unless (constant_defined? && value_matches?)
      end.join(" and ")
    end
    
  end
end

Custom matchersconstant_defined.rb

module CustomMatchers

  def define_constant(expected)
    DefineConstant.new(expected)
  end

  class DefineConstant
    def initialize(expected_constant)
      @expected_constant = expected_constant
    end

    def matches?(actual_object)
      @actual_object = actual_object.is_a?(Class) ? actual_object : actual_object.class
      constant_defined? && value_matches?  
    end
    
    # default value for the constant
    def with_value(value)
      @value = value
      self
    end
    
    def failure_message
      "expected " + error_messages
    end
    
    def negative_failure_message
      "did not expect " + error_messages
    end
    
    def description
      [].tap do |array|
        array << "define constant #{@expected_constant}"
        array << "with value of #{@value}" if instance_variable_defined?("@value") && value_matches?
      end.join(" ")
    end
    
    private
    
    def constant_defined?
      @actual_object.const_defined?(@expected_constant.to_sym)
    end 
    
    def value_matches?
      instance_variable_defined?("@value") ? @actual_object.const_get(@expected_constant.to_sym) == @value : true
    end
    
    def error_messages
      [].tap do |array|
        array << "#{@actual_object} to define constant #{@expected_constant.to_sym}" unless constant_defined?
        array << "#{@expected_constant.to_sym} to have value #{@value}" unless (constant_defined? && value_matches?)
      end.join(" and ")
    end
    
  end
end

suppress_warnings.rb

def suppress_warnings
    original_verbosity = $VERBOSE
    begin
      $VERBOSE = nil
      yield
    ensure
      $VERBOSE = original_verbosity
    end
  end

with_constants.rb

def parse(constant)
  source, _, constant_name = constant.to_s.rpartition('::')

  [source.constantize, constant_name]
end

def with_constants(constants, &block)
  saved_constants = {}
  constants.each do |constant, val|
    source_object, const_name = parse(constant)

    saved_constants[constant] = source_object.const_get(const_name)
    Kernel::silence_warnings { source_object.const_set(const_name, val) }
  end

  begin
    block.call
  ensure
    constants.each do |constant, val|
      source_object, const_name = parse(constant)

      Kernel::silence_warnings { source_object.const_set(const_name, saved_constants[constant]) }
    end
  end
end