// TLD with a wildcard rule and exceptions.
    checkPublicSuffix("ck", null)
    checkPublicSuffix("test.ck", null)
    checkPublicSuffix("b.test.ck", "b.test.ck")
    checkPublicSuffix("a.b.test.ck", "b.test.ck")
    checkPublicSuffix("www.ck", "www.ck")
    checkPublicSuffix("www.www.ck", "www.ck")
    // US K12.
    checkPublicSuffix("us", null)
    checkPublicSuffix("test.us", "test.us")