### Question:
IntegerValue extends Value { @Override Value negate () { return new IntegerValue (-intValue ()); } IntegerValue(int value);   IntegerValue(String value); @Override String toString();  }### Answer:
@Test public void testNegate () { assertEquals ("0", mZeroValue.negate ().toString ()); assertEquals ("-123", mPositiveValue.negate ().toString ()); assertEquals ("123", mNegativeValue.negate ().toString ()); }