### Question:
RealValue extends Value { @Override StringValue toStringValue () { return new StringValue (toString ()); } RealValue(double value);   RealValue(String value); @Override String toString();  }### Answer:
@Test public void testToStringValue () { assertEquals ("-1,23", mNegativeValue.toStringValue ().toString ()); assertEquals ("0", mZeroValue.toStringValue ().toString ()); assertEquals ("1,23", mPositiveValue.toStringValue ().toString ()); }