* {@link FlowBlock#compaction()}
*/
@Test
public void compaction_mandatoryStop() {
FlowGraphGenerator gen = new FlowGraphGenerator();
gen.defineInput("in1");
gen.defineOperator("op1", "in", "out");
gen.defineOperator("op2", "in", "out", ObservationCount.AT_LEAST_ONCE);
gen.defineOutput("out1");
gen.connect("in1", "op1").connect("op1", "op2").connect("op2", "out1");
FlowBlock bin = FlowBlock.fromPorts(