require 'set'

legal_paths = Set['A/B/C', 'A/D/E', 'A/F/G']
Dir.glob('**/system.log').each do |fd|
    if failed_tests_path.include?(fd) #fd for example = A/F/G/E/system.log, A/B/C/K/system.log etc...
        puts fd
    end
end