@Test
    public void decimalToJson() throws IOException {
        JsonNode converted = parse(converter.fromConnectData(TOPIC, Decimal.schema(2), new BigDecimal(new BigInteger("156"), 2)));
        validateEnvelope(converted);
        assertEquals(parse("{ \"type\": \"bytes\", \"optional\": false, \"name\": \"org.apache.kafka.connect.data.Decimal\", \"version\": 1, \"parameters\": { \"scale\": \"2\" } }"),
                converted.get(JsonSchema.ENVELOPE_SCHEMA_FIELD_NAME));
        assertTrue(converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME).isTextual(), "expected node to be base64 text");
        assertArrayEquals(new byte[]{0, -100}, converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME).binaryValue());
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java