testing the publish_message method of the RabbitMQProducer
Published: 2023-06-27 23:23:59

# Testing the RabbitMQProducer `publish_message` Method

In our previous blog post, we discussed how to publish messages to RabbitMQ using the `RabbitMQProducer` class. In this blog post, we will focus on testing the `publish_message` method of the `RabbitMQProducer` class to ensure that it functions as expected.

## Setting Up the Test

To begin with, we need to set up the necessary test environment. We will be using the `unittest.mock` module to create mock objects for testing. Additionally, we will capture the output using the `capsys` fixture provided by pytest.

```python
from pika.exceptions import ConnectionClosedByBroker
from producers.base import RabbitMQProducer
from unittest.mock import MagicMock
```

## Testing the Successful Message Publishing

Let's start by testing the case where the message publishing is successful. We will create a mock `connection` object and a `RabbitMQProducer` instance with the mock connection. Then, we will mock the `channel` object and its `exchange_declare` and `basic_publish` methods. Finally, we will call the `publish_message` method with appropriate arguments.

```python
def test_publish_message(capsys):
    connection = MagicMock()
    producer = RabbitMQProducer(connection)

    channel = MagicMock()
    channel.exchange_declare.return_value = None
    channel.basic_publish.return_value = None

    connection.get_channel.return_value = channel

    exchange = "test_exchange"
    routing_key = "test_routing_key"
    data = {"key": "value"}

    producer.publish_message(exchange=exchange, routing_key=routing_key, data=data)

    channel.basic_publish.assert_called_once()
    channel.exchange_declare.assert_called_once()

    captured = capsys.readouterr()
    assert captured.out.startswith("Message sent to exchange: ")
```

In the test function, we create a mock `connection` object and a `RabbitMQProducer` instance with the mock connection. Then, we create a mock `channel` object and specify the return values for its `exchange_declare` and `basic_publish` methods. Next, we assign the mock `channel` object to the connection's `get_channel` method. After that, we define the exchange, routing key, and data for the message. Finally, we call the `publish_message` method of the producer and assert that the `basic_publish` and `exchange_declare` methods were called once.

## Testing the Failed Message Publishing

Now, let's test the case where the message publishing fails. We will use the `side_effect` property of the `basic_publish` method to raise a `ConnectionClosedByBroker` exception. This will simulate a scenario where the connection is closed by the broker.

```python
def test_publish_message_failed(capsys):
    connection = MagicMock()
    producer = RabbitMQProducer(connection)

    channel = MagicMock()
    channel.exchange_declare.return_value = None
    channel.basic_publish.return_value = None

    def side_effect(exchange, routing_key, body, properties):
        raise ConnectionClosedByBroker(0, "sample")

    channel.basic_publish.side_effect = side_effect
    connection.get_channel.return_value = channel

    exchange = "test_exchange"
    routing_key = "test_routing_key"
    data = {"key": "value"}

    producer.publish_message(exchange=exchange, routing_key=routing_key, data=data)

    captured = capsys.readouterr()
    assert captured.out.startswith("Connection closed by broker. Failed to publish the message")
```

In this test function, we set up the same mock `connection` and `producer` objects. We also create a mock `channel` object and specify its return values. However, this time

, we define a `side_effect` function that raises a `ConnectionClosedByBroker` exception when called. We assign this `side_effect` function to the `basic_publish` method of the `channel` object. Finally, we call the `publish_message` method of the `producer` and assert that the expected error message is printed.

## Running the Tests

To run the tests, we can use a test runner such as `pytest`. With `pytest`, simply execute the following command in your terminal:

```
pytest -v
```

The `-v` flag enables verbose mode, which provides more detailed output during test execution.

## Conclusion

In this blog post, we have covered how to test the `publish_message` method of the `RabbitMQProducer` class. By testing both the successful and failed scenarios, we can ensure that our message publishing functionality works correctly and handles errors gracefully. Properly testing our code helps identify and address any issues or bugs, ensuring the reliability and stability of our RabbitMQ messaging system.