Writing Tests for a Kafka Consumer

You can accomplish a great deal by implementing your own Kafka consumers. Like almost any source code, it is a good idea to build unit tests to verify the functionality of your consumer code. Kafka’s `MockConsumer` test fixture simplifies the process of building unit tests for producer code. In this lab, we will work with consumer test fixtures by writing a few unit tests for an existing consumer.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Clone the Starter Project from GitHub and Perform a Test Run

Clone the starter project from GitHub:

cd ~/
git clone https://github.com/linuxacademy/content-ccdak-consumer-tests-lab.git

Perform a test run to make sure the code is able to compile and run:
```
cd content-ccdak-consumer-tests-lab
./gradlew test
```
The code should compile, but the tests should fail since they are not implemented yet.

Implement the Unit Tests for the `MemberSignupsConsumer`

Edit the test class for MemberSignupsConsumer:

vi src/test/java/com/linuxacademy/ccdak/consumer/MemberSignupsConsumerTest.java

Implement the testHandleRecords_output test:

@Test
public void testHandleRecords_output() {
    // Verify that the testHandleRecords writes the correct data to System.out
    // A text fixture called systemOutContent has already been set up in this class to capture System.out data.
    String topic = "member_signups";
    ConsumerRecord<Integer, String> record = new ConsumerRecord<>(topic, 0, 1, 2, "ROSENBERG, WILLOW");
    Map<TopicPartition, List<ConsumerRecord<Integer, String>>> records = new LinkedHashMap<>();
    records.put(new TopicPartition(topic, 0), Arrays.asList(record));
    ConsumerRecords<Integer, String> consumerRecords = new ConsumerRecords<>(records);

    memberSignupsConsumer.handleRecords(consumerRecords);
    Assert.assertEquals("key=2, value=ROSENBERG, WILLOW, topic=member_signups, partition=0, offset=1n", systemOutContent.toString());
}

Implement the testHandleRecords_none test:

@Test
public void testHandleRecords_none() {
    // Verify that testHandleRecords behaves correctly when processing no records.
    // A text fixture called systemOutContent has already been set up in this class to capture System.out data.
    String topic = "member_signups";
    Map<TopicPartition, List<ConsumerRecord<Integer, String>>> records = new LinkedHashMap<>();
    records.put(new TopicPartition(topic, 0), Arrays.asList());
    ConsumerRecords<Integer, String> consumerRecords = new ConsumerRecords<>(records);

    memberSignupsConsumer.handleRecords(consumerRecords);
    Assert.assertEquals("", systemOutContent.toString());
}

Implement the testHandleRecords_multiple test:

@Test
public void testHandleRecords_multiple() {
    // Verify that testHandleRecords behaves correctly when processing multiple records.
    // A text fixture called systemOutContent has already been set up in this class to capture System.out data.
    String topic = "member_signups";
    ConsumerRecord<Integer, String> record1 = new ConsumerRecord<>(topic, 0, 1, 2, "ROSENBERG, WILLOW");
    ConsumerRecord<Integer, String> record2 = new ConsumerRecord<>(topic, 3, 4, 5, "HARRIS, ALEXANDER");
    Map<TopicPartition, List<ConsumerRecord<Integer, String>>> records = new LinkedHashMap<>();
    records.put(new TopicPartition(topic, 0), Arrays.asList(record1, record2));
    ConsumerRecords<Integer, String> consumerRecords = new ConsumerRecords<>(records);

    memberSignupsConsumer.handleRecords(consumerRecords);
    Assert.assertEquals("key=2, value=ROSENBERG, WILLOW, topic=member_signups, partition=0, offset=1nkey=5, value=HARRIS, ALEXANDER, topic=member_signups, partition=3, offset=4n", systemOutContent.toString());
}

Run your tests and make sure they pass:
```
./gradlew test
```

What are Hands-on Labs

Hands-on Labs are real environments created by industry experts to help you learn. These environments help you gain knowledge and experience, practice without compromising your system, test without risk, destroy without fear, and let you learn from your mistakes. Hands-on Labs: practice your skills before delivering in the real world.

Writing Tests for a Kafka Consumer

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