@Test
public void withJsonBody() throws Exception {

    RequestBody body = RequestBody.create(MediaType.parse("application/json"), "{\"key\":\"value\"}");
    Request request = new Request.Builder()
          .url("https://some.test.api.com")
          .post(body)
          .build();
    Request signed = oauth1.signRequest(request);
    assertAuthHeader(signed, "PvXMVlSUE38kti5PXeIU6kNtg4U%3D");
}