filters-test.kt

val addExtraHeaderFilter = Filter { next ->
    {
        next(it).header("x-extra-header", "some value")
    }
}

@Test
fun adds_a_special_header() {
    val handler: HttpHandler = addExtraHeaderFilter.then { Response(OK) }
    val response: Response = handler(Request(GET, "/echo"))
    assertThat(response, hasStatus(OK)
      .and(hasHeader("x-extra-header", "some value")))
}