### Question:
Atom extends LTLFormula { @Override public String toString(){ return LTLFormula.refToString.get(this); } private  Atom(); static Atom get(String name); @Override LTLType getLTLType(); @Override boolean equals(Object o); @Override int compareTo(Object o); @Override LTLFormula copy(); @Override String toString(); @Override void subFormulae(LinkedHashSet acc); @Override ATransition d(HashMap<LTLFormula, ATransition> D);  }### Answer:
@Test public void testToString() { assertEquals("a", a.toString()); assertEquals("b", b.toString()); }