[← Acknowledgement](06-acknowledgement.md) · [Module README](../README.md)

# 7. Testing without installing Kafka

Two options, both real brokers, and the choice is less obvious than it looks.

## `@EmbeddedKafka` — a real broker inside the JVM

```java
@SpringBootTest
@EmbeddedKafka(topics = "orders", partitions = 3)
class KeysAndPartitionsTest { ... }
```

`spring-kafka-test` starts `EmbeddedKafkaKraftBroker` — the actual Apache Kafka broker classes,
in KRaft mode, in-process. No ZooKeeper, no container, no daemon. It binds a random port and
exposes it as `${spring.embedded.kafka.brokers}`:

```yaml
spring:
  kafka:
    bootstrap-servers: ${spring.embedded.kafka.brokers}
```

It starts in about three seconds and needs nothing installed, which is why every transcript in
this module came from it and why `./scripts/run-all.sh` works on a machine with no Docker.

## Testcontainers — the image you actually deploy

```java
@TestConfiguration(proxyBeanMethods = false)
public class TestcontainersConfiguration {

    @Bean
    @ServiceConnection
    KafkaContainer kafkaContainer() {
        return new KafkaContainer(DockerImageName.parse("apache/kafka:4.1.0"));
    }

}
```

`@ServiceConnection` registers the container's bootstrap servers as the application's, which
removes the `@DynamicPropertySource` block that older examples all carry.

**Two coordinates changed recently and both will bite you:**

```xml
<!-- NOT org.testcontainers:kafka, which stopped at 1.21.4 -->
<dependency>
  <groupId>org.testcontainers</groupId>
  <artifactId>testcontainers-kafka</artifactId>
  <scope>test</scope>
</dependency>
```

Testcontainers 2.x prefixed every module artifact with `testcontainers-`, and Boot 4.1.1 imports
`testcontainers-bom` 2.0.5, which manages only the new names. Using the old coordinate fails
with a Maven error that does not mention the rename:

```
'dependencies.dependency.version' for org.testcontainers:kafka:jar is missing
```

The class moved too: use `org.testcontainers.kafka.KafkaContainer` (Apache Kafka, KRaft), not
the older `org.testcontainers.containers.KafkaContainer` (Confluent images, ZooKeeper).

## Which to use

| | `@EmbeddedKafka` | Testcontainers |
|---|---|---|
| startup | ~3s | ~10s, plus image pull |
| needs Docker | no | yes |
| broker version | the client library's | whatever image you name |
| TLS, SASL, quotas, partitions | not modelled | real |

Use `@EmbeddedKafka` for the bulk of a suite and Testcontainers for the handful of tests where
the difference between "the broker classes" and "the broker you deploy" matters. The
[`TestcontainersConfiguration`](../src/test/java/com/ankurm/kafkabasics/TestcontainersConfiguration.java)
in this module is compiled but not exercised by `run-all.sh`, because the machine that
regenerates `docs/output/` has no Docker daemon &mdash; which is itself the argument for keeping
both paths.

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