Operator op2 = new OP_Filter("mmm2", pattern);
Operator op3 = new OP_Join("mmm3", pattern);
pattern.add(op1);
pattern.add(op2);
pattern.add(op3);
pattern.connect(op1, op3);
pattern.connect(op2, op3);
Rule r = new SillyRule("basic", pattern);
List<OperatorPlan> l = r.match(plan);
assertEquals(1, l.size());