### Question:
ApiRequest { Map<String, String> getHeaders() { return headers; } private  ApiRequest(Builder builder);   }### Answer:
@Test public void addHeader_verifyHeaders() { ApiRequest apiRequest = new ApiRequest.Builder(ApiRequest.RequestMethod.POST, "/") .addHeader("header_key", "header_value") .build(); Map<String, String> headers = apiRequest.getHeaders(); assertEquals("header_value", headers.get("header_key")); assertEquals(1, headers.size()); }