How to have KafkaProducer to use a mock Schema Reg

Question

I'm using KafkaProducer in my test cases and my producer uses the schemaRegistryUrl which points a my local instance of Schema Registry. Is there a way to mock how KafkaProducer connects with the Schema Registry? That is, to have KafkaProducer/Consumer in my tests to work without a running instance of Schema Registry.

Answer 1

Here is an example of stubbing and mocking but with spring cloud stream. Look at the src/test/java/com/example/cloud/avro/ folder.

Answer 2

There absolutely is. The KafkaAvroSerializer and KafkaAvroDeserializer both have a constructor that takes in a SchemaRegistryClient. You can use a MockSchemaRegistryClient as the SchemaRegistryClient. Here's a code snippet showing how to do that:

private MockSchemaRegistryClient mockSchemaRegistryClient = new MockSchemaRegistryClient();
private String registryUrl = "unused";

public <T> Serde<T> getAvroSerde(boolean isKey) {
    return Serdes.serdeFrom(getSerializer(isKey), getDeserializer(isKey));
}

private <T> Serializer<T> getSerializer(boolean isKey) {
    Map<String, Object> map = new HashMap<>();
    map.put(KafkaAvroDeserializerConfig.AUTO_REGISTER_SCHEMAS, true);
    map.put(KafkaAvroDeserializerConfig.SCHEMA_REGISTRY_URL_CONFIG, registryUrl);
    Serializer<T> serializer = (Serializer) new KafkaAvroSerializer(mockSchemaRegistryClient);
    serializer.configure(map, isKey);
    return serializer;
}

private <T> Deserializer<T> getDeserializer(boolean key) {
    Map<String, Object> map = new HashMap<>();
    map.put(KafkaAvroDeserializerConfig.SPECIFIC_AVRO_READER_CONFIG, "true");
    map.put(KafkaAvroDeserializerConfig.SCHEMA_REGISTRY_URL_CONFIG, registryUrl);
    Deserializer<T> deserializer = (Deserializer) new KafkaAvroDeserializer(mockSchemaRegistryClient);
    deserializer.configure(map, key);
    return deserializer;
}