describe('a', function() {
  this.timeout(5000);
  this.slow();

  it('1', function(cb) {
    setTimeout(cb, 3000);
  });

  it('2', function(cb) {
    this.slow(); // just for contrast with test 1
    setTimeout(cb, 3000);
  });
});

If I understand the docs correctly, I expect neither of the tests to timeout or have slow warnings because they're both covered by this.timeout and this.slow calls in the describe section. Neither of the tests timeout, but the first test (not covered by its own redundant this.slow) has a slow warning still:

  a
    ✓ 1 (3008ms)
    ✓ 2


  2 passing (6s)

mocha version 2.5.3