### Question:
FieldAndRValue implements Serializable { @Override public String toString() { return field + ":" + rvalue; } FieldAndRValue();  FieldAndRValue(Path field, RValueExpression rvalue); Path getField(); void setField(Path p); RValueExpression getRValue(); void setRValue(RValueExpression e); @Override String toString(); @Override int hashCode(); @Override boolean equals(Object obj);  }### Answer:
@Test public void testToString() { FieldAndRValue instance = new FieldAndRValue(); String expResult = "null:null"; String result = instance.toString(); assertEquals(expResult, result); Path p = new Path("ToString"); RValueExpression rve = new RValueExpression(p); instance = new FieldAndRValue(p, rve); expResult = "ToString:{\"$valueof\":\"ToString\"}"; result = instance.toString(); assertEquals(expResult, result); }