sclass Test_PairCollector { PairCollector collector; S result; void makeCollector { collector = new PairCollector; swap method collector.complete(a, b) { result = "Got " + a + " + " + b; } result = null; } run { makeCollector(); collector.setA("Hello"); assertNull(result); collector.setB(123); assertEqualsVerbose(result, "Got Hello + 123"); makeCollector(); collector.setterForB().get(456); assertNull(result); collector.setterForA().get("Yo"); assertEqualsVerbose(result, "Got Yo + 456"); } }