How do you define Mocha tests programmatically and asynchronously?

I'm trying to integrate some programmatically generated tests with the Mocha test framework in node.js.

var Promise = require('promise');

var resolved = Promise.resolve(true);

suite("Synchronously defined suite", function() {
  test("Synchronously defined test", function() {
    return resolved;
  });
});

defer(function() {
  suite("Asynch DEFINED test", function() {
    suiteSetup(function() {
      console.log("Asynch setupSuite running...");
    });

    test("Asynch Test", function() {
      console.log("Async test running...");
      return resolved;
    });
  });
});

function defer(fn) {
  console.log("Calling defer...");
  setTimeout(fn, 100);
}

When I execute this I get:

$ mocha --ui tdd nested-test.js 
Calling defer...


  Synchronously defined suite
    ✓ Synchronously defined test


  1 passing (4ms)

It seems that Mocha requires that all "suite" functions be executed synchronously at module load time - deferred calls seem to be (silently) ignored (or the program exits before calling them).