text: import test from 'ava';
  import sut from './index';
  
  test('undefined is an empty string', t => t.true(sut()));
  
  test('"" is an empty string', t => t.true(sut('')));
  
  test('Single whitespace is not empty', t => t.false(sut(' ')));
  
  test('Whitespace is not empty', t => t.false(sut('\n\n\t')));
  
  test('words are not empty', t => t.false(sut('a')));
  