### Question:
GroupTransition { @Override public String toString() { return new StringBuilder(groupIn).append(TRANSITION).append(groupOut).toString(); } GroupTransition(String groupIn, String groupOut); String getIn(); String getOut(); @Override int hashCode(); @Override boolean equals(Object object); @Override String toString();  }### Answer:
@Test void testToString() { assertEquals("a -> b", new GroupTransition("a", "b").toString()); }