@Test
public void testAddRemoveContains() {

    assertFalse(AHashSet.empty ().contains("a"));
    assertTrue (AHashSet.empty ().with("a").contains("a"));
    assertFalse(AHashSet.empty ().with("a").contains("b"));
    assertTrue (AHashSet.empty ().with("a").with("b").contains("b"));
    assertFalse(AHashSet.empty ().with("a").with("b").contains("c"));
    assertFalse(AHashSet.empty ().with("a").with("b").without("a").contains("a"));
    assertTrue (AHashSet.empty ().with("a").with("b").without("a").contains("b"));
    assertFalse(AHashSet.empty ().with("a").with("b").without("a").contains("c"));
}