DoubletonSetTest - Original

private void assertUnchanged() {
    Verify.assertSize(2, this.set);
    Verify.assertContainsAll(this.set, "1", "2");
    Verify.assertNotContains("3", this.set);
}

@Test
public void addDuplicate() {
    try {
        this.set.add("1");
        Assert.fail("Cannot add to DoubletonSet");
    } catch (UnsupportedOperationException ignored) {
        this.assertUnchanged();
    }
}