@Test
    void requireThatAddAllWorksAsExpected() {
        Headers headers = new Headers();
        headers.add("foo", "bar");
        headers.add("bar", "baz");
        assertEquals(List.of("bar"), headers.get("foo"));
        assertEquals(List.of("baz"), headers.get("bar"));

        Map<String, List<String>> map = Map.of("foo", List.of("baz", "cox"), "bar", List.of("cox"));
        headers.addAll(map);

        assertEquals(List.of("bar", "baz", "cox"), headers.get("foo"));
        assertEquals(List.of("baz", "cox"), headers.get("bar"));
    }
@author Simon Thoresen Hult
@author Einar M R Rosenvinge
application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java