Testing RabbitMQConsumerBase class
Published: 2023-06-27 23:25:51

# Testing the RabbitMQConsumerBase `consume` Method

In our previous blog post, we discussed how to create a RabbitMQ consumer using the `RabbitMQConsumerBase` class. In this blog post, we will focus on testing the `consume` method of the `RabbitMQConsumerBase` class to ensure that it performs the necessary steps for consuming messages from RabbitMQ.

## Setting Up the Test

To begin with, we need to set up the necessary test environment. We will be using the `pytest` framework for our tests and the `unittest.mock` module to create mock objects. Additionally, we will use the `pytest-mock` plugin to simplify the creation of mock objects.

```python
import pytest
from unittest.mock import MagicMock, ANY
from consumers.base import RabbitMQConsumerBase
from config import Config
```

We will also define a sample subclass of `RabbitMQConsumerBase` called `SampleRabbitMQConsumer` for testing purposes.

```python
class SampleRabbitMQConsumer(RabbitMQConsumerBase):
    def process_message(self, channel, method, properties, body):
        pass
```

Next, we will create a fixture called `consumer_mock` using the `pytest.fixture` decorator. This fixture will set up a `SampleRabbitMQConsumer` instance and a mock `connection` object. The `mocker` parameter is used to create the mock objects.

```python
@pytest.fixture
def consumer_mock(mocker):
    consumer = SampleRabbitMQConsumer("name", "sample", "sample", 0, "sample", "sample")
    connection_mock = MagicMock()

    connection_context_mock = mocker.patch("connection.RabbitMQConnection.__enter__")
    connection_context_mock.return_value = connection_mock

    return consumer, connection_mock
```

Now, we are ready to write individual tests for the `consume` method.

## Testing Exchange Declaration

The first step in the `consume` method is to declare the exchange. We can test this by asserting that the `exchange_declare` method is called on the mock `channel` object with the correct arguments.

```python
def test_consume_exchange_declared(consumer_mock):
    config = Config()
    consumer, connection_mock = consumer_mock
    consumer.consume()

    assert connection_mock.get_channel.return_value.exchange_declare.call_count == 1
    connection_mock.get_channel.return_value.exchange_declare.assert_called_with(
        exchange_type="topic",
        exchange=config.EXCHANGE_NAME
    )
```

## Testing Queue Declaration

The next step is to declare the queue. We can test this by asserting that the `queue_declare` method is called on the mock `channel` object with the correct arguments.

```python
def test_consume_queue_declared(consumer_mock):
    consumer, connection_mock = consumer_mock
    consumer.consume()

    assert connection_mock.get_channel.return_value.queue_declare.call_count == 1
    connection_mock.get_channel.return_value.queue_declare.assert_called_with(
        queue="name"
    )
```

## Testing Queue Binding

After declaring the queue, the next step is to bind it to the exchange. We can test this by asserting that the `queue_bind` method is called on the mock `channel` object with the correct arguments.

```python
def test_consume_queue_bind(consumer_mock):
    config = Config()
    consumer, connection_mock = consumer_mock
    consumer.consume()

    assert connection_mock.get_channel.return_value.queue_bind.call_count == 1
    connection_mock.get_channel.return_value.queue_bind.assert_called_with(
        queue="name", exchange=config.EXCHANGE_NAME, routing_key="sample"
    )
```

## Testing Basic Consume

Once the queue is bound to the exchange, we can

 start consuming messages. We can test this by asserting that the `basic_consume` method is called on the mock `channel` object with the correct arguments.

```python
def test_consume_basic_consume(consumer_mock):
    consumer, connection_mock = consumer_mock
    consumer.consume()

    assert connection_mock.get_channel.return_value.basic_consume.call_count == 1
    connection_mock.get_channel.return_value.basic_consume.assert_called_with(
        queue="name",
        auto_ack=False,
        on_message_callback=ANY,
    )
```

## Testing Start Consuming

The `consume` method should start consuming messages by calling the `start_consuming` method on the mock `channel` object. We can test this by asserting that the `start_consuming` method is called.

```python
def test_consume_uses_start_consuming(consumer_mock):
    consumer, connection_mock = consumer_mock
    consumer.consume()

    assert connection_mock.get_channel.return_value.start_consuming.call_count == 1
```

## Testing Interrupted Consumption

We should also test the scenario where the consumption is interrupted, such as when a `KeyboardInterrupt` occurs. In this case, the `stop_consuming` method should be called on the mock `channel` object.

```python
def test_consume_uses_start_consuming_interrupted(consumer_mock):
    consumer, connection_mock = consumer_mock
    connection_mock.get_channel.return_value.start_consuming.side_effect = KeyboardInterrupt
    consumer.consume()

    assert connection_mock.get_channel.return_value.stop_consuming.call_count == 1
```

## Conclusion

In this blog post, we have covered the testing of the `consume` method of the `RabbitMQConsumerBase` class. By testing each step of the consumption process, we can ensure that messages are consumed correctly from RabbitMQ. Properly testing our consumer helps identify and address any issues or bugs, ensuring the reliability and stability of our RabbitMQ messaging system.