@Test
    void requireThatGetFirstWorksAsExpected() {
        Headers headers = new Headers();
        assertNull(headers.getFirst("foo"));
        headers.add("foo", List.of("bar", "baz"));
        assertEquals("bar", headers.getFirst("foo"));
    }
@author Simon Thoresen Hult
@author Einar M R Rosenvinge
application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java