Try something like this:
[tester tapScreenAtPoint:CGPointMake(160.0, 284.0)];
[tester waitForTimeInterval:0.1];
[tester tapScreenAtPoint:CGPointMake(160.0, 284.0)];
[tester waitForTimeInterval:5.0];
The important parts are a short wait on the tester between taps and then a long wait on the tester after the taps in order for the gesture to be recognized and processed.