@Test
  public void testCustomParameterPassThrough() throws Exception {
    try (LocalTestServerContext sc =
        new LocalTestServerContext(
            "\n"
                + "{\n"
                + "   \"results\" : [\n"
                + "      {\n"
                + "         \"address_components\" : [\n"
                + "            {\n"
                + "               \"long_name\" : \"Google Building 41\",\n"
                + "               \"short_name\" : \"Google Bldg 41\",\n"
                + "               \"types\" : [ \"premise\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"1600\",\n"
                + "               \"short_name\" : \"1600\",\n"
                + "               \"types\" : [ \"street_number\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"Amphitheatre Parkway\",\n"
                + "               \"short_name\" : \"Amphitheatre Pkwy\",\n"
                + "               \"types\" : [ \"route\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"Mountain View\",\n"
                + "               \"short_name\" : \"Mountain View\",\n"
                + "               \"types\" : [ \"locality\", \"political\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"Santa Clara County\",\n"
                + "               \"short_name\" : \"Santa Clara County\",\n"
                + "               \"types\" : [ \"administrative_area_level_2\", \"political\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"California\",\n"
                + "               \"short_name\" : \"CA\",\n"
                + "               \"types\" : [ \"administrative_area_level_1\", \"political\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"United States\",\n"
                + "               \"short_name\" : \"US\",\n"
                + "               \"types\" : [ \"country\", \"political\" ]\n"
                + "            },\n"
                + "            {\n"
                + "               \"long_name\" : \"94043\",\n"
                + "               \"short_name\" : \"94043\",\n"
                + "               \"types\" : [ \"postal_code\" ]\n"
                + "            }\n"
                + "         ],\n"
                + "         \"formatted_address\" : \"Google Bldg 41, 1600 Amphitheatre Pkwy, Mountain View, CA 94043, USA\",\n"
                + "         \"geometry\" : {\n"
                + "            \"bounds\" : {\n"
                + "               \"northeast\" : {\n"
                + "                  \"lat\" : 37.4228642,\n"
                + "                  \"lng\" : -122.0851557\n"
                + "               },\n"
                + "               \"southwest\" : {\n"
                + "                  \"lat\" : 37.4221145,\n"
                + "                  \"lng\" : -122.0859841\n"
                + "               }\n"
                + "            },\n"
                + "            \"location\" : {\n"
                + "               \"lat\" : 37.4224082,\n"
                + "               \"lng\" : -122.0856086\n"
                + "            },\n"
                + "            \"location_type\" : \"ROOFTOP\",\n"
                + "            \"viewport\" : {\n"
                + "               \"northeast\" : {\n"
                + "                  \"lat\" : 37.4238383302915,\n"
                + "                  \"lng\" : -122.0842209197085\n"
                + "               },\n"
                + "               \"southwest\" : {\n"
                + "                  \"lat\" : 37.4211403697085,\n"
                + "                  \"lng\" : -122.0869188802915\n"
                + "               }\n"
                + "            }\n"
                + "         },\n"
                + "         \"place_id\" : \"ChIJxQvW8wK6j4AR3ukttGy3w2s\",\n"
                + "         \"types\" : [ \"premise\" ]\n"
                + "      }\n"
                + "   ],\n"
                + "   \"status\" : \"OK\"\n"
                + "}\n")) {
      String address = "1600 Amphitheatre Parkway, Mountain View, CA";
      GeocodingResult[] results =
          GeocodingApi.newRequest(sc.context)
              .address(address)
              .custom("new_forward_geocoder", "true")
              .await()
              .results;

      assertNotNull(Arrays.toString(results));
      assertEquals(
          "Google Bldg 41, 1600 Amphitheatre Pkwy, Mountain View, CA 94043, USA",
          results[0].formattedAddress);

      sc.assertParamValue(address, "address");
      sc.assertParamValue("true", "new_forward_geocoder");
    }
  }
Testing custom parameter pass through.

<p>See <a
href="https://googlegeodevelopers.blogspot.com.au/2016/11/address-geocoding-in-google-maps-apis.html">
Address Geocoding in the Google Maps APIs</a> for the reasoning behind this usage.
src/test/java/com/google/maps/GeocodingApiTest.java