Do protestants believe that the New Testament is the final covenant? Do Protestants believe that the New Testament is the final covenant/testament? For example, many branches which built off Christianity believe the Bible is not complete and requires another revelation/modification from Jesus Christ (i.e. Mormonism, JW's) 

If so, what are the arguments / biblical basis used to support this view?
Article VI of the Articles of Religion of the Church of England, which is accepted by most of the Anglican Communion, provides in part,  that


  HOLY Scripture containeth all things necessary to salvation: so that whatsoever is not read therein, nor may be proved thereby, is not to be required of any man, that it should be believed as an article of the Faith, or be thought requisite or necessary to salvation. ... 


Lutherans hold to the same viewpoint.