public void assertNonNegative() {
		if(value < 0)
			throw new IllegalStateException("non negative value required");
	}
@Test()
    public void zeroQuantity_passesOnCheckForNonNegative() throws Exception {
        Quantity<Metrics> zero = new Quantity<Metrics>(0, Metrics.cm);
        zero.assertNonNegative();
    }