@Test
    public void highPrecisionNumericDecimalToConnect() {
        // this number is too big to be kept in a float64!
        BigDecimal reference = new BigDecimal("1.23456789123456789");
        Schema schema = Decimal.schema(17);
        String msg = "{ \"schema\": { \"type\": \"bytes\", \"name\": \"org.apache.kafka.connect.data.Decimal\", \"version\": 1, \"parameters\": { \"scale\": \"17\" } }, \"payload\": 1.23456789123456789 }";
        SchemaAndValue schemaAndValue = converter.toConnectData(TOPIC, msg.getBytes());
        assertEquals(schema, schemaAndValue.schema());
        assertEquals(reference, schemaAndValue.value());
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java