### Question:
RealValue extends Value { @Override Value negate () { mValue = -mValue; return this; } RealValue(double value);   RealValue(String value); @Override String toString();  }### Answer:
@Test public void testNegate () { assertEquals ("-0", mZeroValue.negate ().toString ()); assertEquals ("-1,23", mPositiveValue.negate ().toString ()); assertEquals ("1,23", mNegativeValue.negate ().toString ()); }