@Test
    public void bytesToJson() throws IOException {
        JsonNode converted = parse(converter.fromConnectData(TOPIC, Schema.BYTES_SCHEMA, "test-string".getBytes()));
        validateEnvelope(converted);
        assertEquals(parse("{ \"type\": \"bytes\", \"optional\": false }"), converted.get(JsonSchema.ENVELOPE_SCHEMA_FIELD_NAME));
        assertEquals(ByteBuffer.wrap("test-string".getBytes()),
                ByteBuffer.wrap(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