Validate offset topic (#20)

src/main/java/com/bakdata/kafka/KafkaConnectorSourceResetter.java

@@ -80,9 +80,9 @@
  * }</pre>
  *
  * Kafka Connect stores offsets for source connectors in a dedicated topic. The key of such an offset consists of the
- * connector name and a connector specific partition name, e.g., {@code ["connector-name", { some-source-specific
- * -data... }] }. This tool finds all partitions belonging to the connector that should be reset and deletes the
- * corresponding offsets.
+ * connector name and a connector specific partition name, e.g.,
+ * {@code ["connector-name", { some-source-specific -data... }] }. This tool finds all partitions belonging to the
+ * connector that should be reset and deletes the corresponding offsets.
  */
 
 @Slf4j
@@ -135,6 +135,7 @@ public void run() {
         log.info("Finished resetting {}", this.sharedOptions.getConnectorName());
     }
 
+
     private void resetPartitions(final Iterable<byte[]> partitions, final Map<String, Object> kafkaConfig) {
         try (final Producer<byte[], byte[]> producer = createProducer(kafkaConfig)) {
             producer.initTransactions();
@@ -179,7 +180,7 @@ private Consumer<byte[], byte[]> createConsumer(final Map<String, Object> kafkaC
         final Deserializer<byte[]> byteArrayDeserializer = new ByteArrayDeserializer();
         final Consumer<byte[], byte[]> consumer =
                 new KafkaConsumer<>(kafkaConfig, byteArrayDeserializer, byteArrayDeserializer);
-        final List<PartitionInfo> partitions = consumer.partitionsFor(this.offsetTopic);
+        final List<PartitionInfo> partitions = this.partitionsForOffsetTopic(consumer);
         final List<TopicPartition> topicPartitions = partitions.stream()
                 .map(KafkaConnectorSourceResetter::toTopicPartition)
                 .collect(Collectors.toList());
@@ -188,4 +189,13 @@ private Consumer<byte[], byte[]> createConsumer(final Map<String, Object> kafkaC
         return consumer;
     }
 
+    private <K, V> List<PartitionInfo> partitionsForOffsetTopic(final Consumer<K, V> consumer) {
+        final Map<String, List<PartitionInfo>> topicsWithPartition = consumer.listTopics();
+        if (!topicsWithPartition.containsKey(this.offsetTopic)) {
+            final String message = String.format("Topic '%s' does not exist.", this.offsetTopic);
+            throw new IllegalArgumentException(message);
+        }
+        return topicsWithPartition.get(this.offsetTopic);
+    }
+
 }

src/test/java/com/bakdata/kafka/KafkaConnectorSourceResetterApplicationTest.java

@@ -123,6 +123,38 @@ void test() throws InterruptedException {
         this.softly.assertThat(valuesAfterReset).hasSize(6);
     }
 
+    @Test
+    void shouldExitOneWhenOffsetTopicIsSetIncorrectly() throws InterruptedException {
+        this.createConnectCluster();
+        delay(10, TimeUnit.SECONDS);
+        final List<String> values = this.kafkaCluster.readValues(ReadKeyValues.from(TOPIC)
+                .with(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class)
+                .with(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class)
+                .build());
+        this.softly.assertThat(values)
+                .hasSize(3);
+        this.connectCluster.stop();
+        delay(10, TimeUnit.SECONDS);
+        final KafkaConnectResetterApplication app = new KafkaConnectResetterApplication();
+
+        final CommandLine commandLine = getCLI(app);
+        final int exitCode = commandLine.execute("source",
+                CONNECTOR_NAME,
+                "--brokers", this.kafkaCluster.getBrokerList(),
+                "--offset-topic", "wrong-offset-topic"
+        );
+        this.softly.assertThat(exitCode)
+                .isEqualTo(1);
+        this.createConnectCluster();
+        delay(10, TimeUnit.SECONDS);
+        final List<String> valuesAfterReset = this.kafkaCluster.readValues(ReadKeyValues.from(TOPIC)
+                .with(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class)
+                .with(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class)
+                .build());
+        this.softly.assertThat(valuesAfterReset)
+                .hasSize(3);
+    }
+
     private void createConnectCluster() {
         this.connectCluster = new EmbeddedConnect(EmbeddedConnectConfig.kafkaConnect()
                 .with(DistributedConfig.OFFSET_STORAGE_TOPIC_CONFIG, OFFSETS)