@Test
public void itShouldCalculateSumWithInts() {
Dollars sum = zero.plus(1);
Assert.assertEquals(one, sum);
}
@Test
public void itShouldReturnItSelfWhenIAddZero() {
Dollars sum = one.plus(zero);
Assert.assertEquals(one, sum);
}
@Test
public void itShouldCalculateSumWithDollars() {
Dollars sum = fraction.plus(one);
Assert.assertEquals(new Dollars(2.75), sum);
}