@Test
    public void decimalToConnect() {
        Schema schema = Decimal.schema(2);
        BigDecimal reference = new BigDecimal(new BigInteger("156"), 2);
        // Payload is base64 encoded byte[]{0, -100}, which is the two's complement encoding of 156.
        String msg = "{ \"schema\": { \"type\": \"bytes\", \"name\": \"org.apache.kafka.connect.data.Decimal\", \"version\": 1, \"parameters\": { \"scale\": \"2\" } }, \"payload\": \"AJw=\" }";
        SchemaAndValue schemaAndValue = converter.toConnectData(TOPIC, msg.getBytes());
        BigDecimal converted = (BigDecimal) schemaAndValue.value();
        assertEquals(schema, schemaAndValue.schema());
        assertEquals(reference, converted);
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java