Returns the caller information String in Rails testing; in default it returns the last caller in *_test.rb so it is useful in assertions in library/module files

rails_get_caller_info_message.rb

  # Returns the String for the caller information
  #
  # @example To display the location of the last caller in the *_test.rb file.
  #    assert abc, sprintf("(%s): abc=%s", _get_caller_info_message, abc.inspect)  # defined in test_helper.rb
  #
  # @example displays the exact line where an error occurs
  #    assert false, _get_caller_info_message(bind_offset: -1, prefix: true)+" Error occurs exactly at this line."
  #
  # @param bind_offset: [Integer, NilClass] offset for caller_locations (used for displaying the caller routine). In default (=nil), the last location in *_test.rb (such as, inside a block). If this is 0, it is useful in the case where this method is called in a test library method that is called from an original test routine. Therefore, specify "-1" to get the information of the caller itself (Second example above).
  # @param fmt: [String] sprintf format. It must contain %s (for path) and %d (or %s) (for line number) in this order.
  # @param prefix: [Boolean] If true (Def: false), the return is enclosed with a pair of parentheses, followed by a colon
  # @return [String]
  def get_caller_info_message(bind_offset: nil, fmt: "%s:%d", prefix: false)
    if !bind_offset
      bind = caller_locations.each{|i| break i if /_test\.rb$/ =~ i.absolute_path }
      if bind.respond_to? :absolute_path
        bind_offset = nil
      else
        bind = nil
        bind_offset = 0  # in failure (meaning when this method is NOT called from a Rails test file)
      end
    end

    bind ||= caller_locations(2+bind_offset, 1)[0]  # Ruby 2.0+

    # NOTE: bind.label returns "block in <class:TranslationIntegrationTest>"
    ret = sprintf fmt, bind.absolute_path.sub(%r@.*(/test/)@, '\1'), bind.lineno
    (prefix ? sprintf("(%s):", ret) : ret)
  end