assertEquals(" f1: bar f2: bar f2: bar", result);
callbacks.remove( fn1 );
callbacks.add( fn1 );
assertEquals(" f1: bar f2: bar f2: bar f1: bar", result);
callbacks.remove( fn1 );
callbacks.disable();
callbacks.add( fn1 );
assertEquals(" f1: bar f2: bar f2: bar f1: bar f1: bar", result);
// Test adding callback functions in nested executions
result = "";