example.spec.js

// this scopes the contents to the current spec
// doesn't matter if callback is fired way later than timeout
it "should work"
  var contents
  fs.readFile('foo', function(err, c){
    contents = c
  })

  wait(-{
    contents.should.eql 'bar'
  }, 50)
end

// the function "callback" (or "async" or whatever) adds a wait
// function to the wait queue that checks if the function is
// called before timeout. also, store the currentSpec to check
// if the scope is still correct if the function fires way too late
it "should work"
  fs.readFile('foo', callback(function(err, contents){
    contents.should.eql 'bar'
  }))
end