### Question:
Circuit { @Override public String toString() { return new StringBuilder().append(type).append(Constant.SPACE).append(groups).toString(); } Circuit(CircuitType type, String groupIn, String groupOut); CircuitType getType(); String getIn(); String getOut(); @Override int hashCode(); @Override boolean equals(Object object); @Override String toString();  }### Answer:
@Test void testToString() { assertEquals(CircuitType.MIDDLE.name() + " a -> b", new Circuit(CircuitType.MIDDLE, "a", "b").toString()); }