Tests always pass

[benpolinsky]

Please correct me if I'm wrong, but it seems the test cases provided will never fail.
This is because you're calling the done() callback with any errors, thus suppressing a possible failed test case.

For example, the following test passes:

it('should preserve order with multiple selectors', function(done){
    Metalsmith('test/fixture')
      .use(markdown())
      .use(headings({ selectors: ['h1', 'h2']}))
      .build(function(err, files){
        if (err) return done(err);
        expect(1).toEqual(2)
        done();
      });
  });

I'd suggest just letting any error through.