def covered_strength
      return 0.0 if empty? || lines_of_code.zero?
      Float(map { |f| f.covered_strength * f.lines_of_code }.inject(:+) / lines_of_code)
    end
def covered_strength
      return 0.0 if empty? || lines_of_code.zero?
      Float(map { |f| f.covered_strength * f.lines_of_code }.inject(:+) / lines_of_code)
    end
Computes the strength (hits / line) based upon lines covered and lines missed
 @return [Float]