I think you need something like:
```javascript
test('...', function(done) {
  var promise = Promise.resolve(true);
  this.sinon.stub(MockSilentSms, 'checkSilentModeFor')
    .returns(promise);
  // trigger message
  promise.then(function() {
    sinon.assert.notCalled();
  }).then(done, done);
}
```

To check that the test is adequate, try to return the promise with "resolve(false)" and see if the test fails.