module Mutest
  # Utility methods
  module Util
    # Error raised by `Util.one` if size is less than zero or greater than one
    SizeError = Class.new(IndexError)

    # Return only element in array if it contains exactly one member
    #
    # @param array [Array]
    #
    # @return [Object] first entry
    def self.one(array)
      return array.first if array.one?

      fail SizeError, "expected size to be exactly 1 but size was #{array.size}"
    end
  end # Util
end # Mutest