public boolean contains(String headerName) {
        String normalName = HeaderName.normalize(Objects.requireNonNull(headerName, "headerName"));
        return findNormal(normalName) != ABSENT;
    }
@Test
    void contains() {
        Headers headers = new Headers();
        headers.add("Via", "duct");
        headers.add("COOKie", "this=that");
        headers.add("cookIE", "frizzle=frazzle");
        headers.add("Soup", "salad");

        assertTrue(headers.contains("CoOkIe"));
        assertTrue(headers.contains(new HeaderName("CoOkIe")));
        assertTrue(headers.contains("cookie"));
        assertTrue(headers.contains(new HeaderName("cookie")));
        assertTrue(headers.contains("Cookie"));
        assertTrue(headers.contains(new HeaderName("Cookie")));
        assertTrue(headers.contains("COOKIE"));
        assertTrue(headers.contains(new HeaderName("COOKIE")));
        assertFalse(headers.contains("Monkey"));
        assertFalse(headers.contains(new HeaderName("Monkey")));

        headers.remove("cookie");
        assertFalse(headers.contains("cookie"));
        assertFalse(headers.contains(new HeaderName("cookie")));
    }