        if(input !== null)
          client.setRequestHeader("Content-Type", input)
        client.send("TEST")
        assert_equals(client.responseText, "TEST")
        assert_equals(client.getResponseHeader("x-request-content-type"), output)
        }, title)
      }

      request(
        "text; charset=ascii",
        "text; charset=ascii",
        "header with invalid MIME type is not changed"
      )
      request(
        "",
        "",
        "header with invalid MIME type (empty string) is not 