def MUST!(m)
      RequirementLevel::High.new(m, false, subject, *challenges).result(true)
    end
def MUST!(m)
      RequirementLevel::High.new(m, false, subject, *challenges).result(true)
    end
@example _Absolute requirement_ definition with isolation
   it { 'foo'.upcase }.MUST! eql 'FOO'

 @see MUST