Testing the connection class
Published: 2023-06-27 15:42:39

Title: Effective Test Cases for RabbitMQConnection with pytest

Table of Contents:
- Overview
- Code
- Test Cases
   - test_singleton_instance
   - test_connect_successful
   - test_connect_failed
   - test_is_connected
   - test_is_connected_false
   - test_close
   - test_get_channel_not_connected
   - test_get_channel_connected
- Conclusion

## Overview
This blog post explores how to write effective test cases for the `RabbitMQConnection` class using the pytest framework. The `RabbitMQConnection` class is responsible for establishing and managing connections to RabbitMQ, a popular message broker. Thoroughly testing this class ensures its functionality and reliability.

## Code
```python
import pytest
from unittest.mock import patch, MagicMock
from pika import BlockingConnection, exceptions
from connection import RabbitMQConnection
from config import Config as AppConfig

@pytest.fixture
def config():
    return AppConfig()

@pytest.fixture
def rabbitmq_connection(config):
    return RabbitMQConnection(
        host=config.RABBITMQ_HOST,
        port=config.RABBITMQ_PORT,
        username=config.RABBITMQ_USER,
        password=config.RABBITMQ_PASSWORD
    )
```

## Test Cases
This section covers each individual test case and its explanation.

### test_singleton_instance
Checks if the `RabbitMQConnection` class behaves as a singleton, ensuring only one instance of the class is created.
```python
def test_singleton_instance():
    connection1 = RabbitMQConnection()
    connection2 = RabbitMQConnection()
    assert connection1 is connection2
```

### test_connect_successful
Verifies that the `connect` method of `RabbitMQConnection` establishes a successful connection.
```python
def test_connect_successful(rabbitmq_connection):
    with patch.object(BlockingConnection, "__init__", return_value=None), patch.object(BlockingConnection, "is_open",
                                                                                       return_value=True):
        rabbitmq_connection.connect()

        assert rabbitmq_connection.connection is not None
        assert rabbitmq_connection.connection.is_open
```

### test_connect_failed
Checks the behavior of the `connect` method when a connection attempt fails.
```python
def test_connect_failed(rabbitmq_connection):
    with patch.object(BlockingConnection, "__init__", side_effect=exceptions.AMQPConnectionError("Connection failed")):
        rabbitmq_connection.connect()

        assert rabbitmq_connection.connection is None
```

### test_is_connected
Verifies the `is_connected` method of `RabbitMQConnection`.
```python
def test_is_connected(rabbitmq_connection):
    with patch.object(BlockingConnection, "__init__", return_value=None), patch.object(BlockingConnection, "is_open",
                                                                                       return_value=True):
        rabbitmq_connection.connect()

        assert rabbitmq_connection.is_connected()
```

### test_is_connected_false
Checks the behavior of the `is_connected` method when no connection is established.
```python
def test_is_connected_false(rabbitmq_connection):
    assert not rabbitmq_connection.is_connected()
```

### test_close
Ensures that the `close` method of `RabbitMQConnection` closes the connection.
```python
def test_close(rabbitmq_connection):
    connection_mock = MagicMock(BlockingConnection)
    rabbitmq_connection.connection = connection_mock

    rabbitmq_connection.close()

    connection_mock.close.assert_called_once()
    assert rabbitmq_connection.connection is None
```

### test_get_channel_not_connected
Checks the behavior of the `get_channel` method when no connection is established.
```python
def test_get_channel_not_connected(rabbitmq_connection):
    assert rabbitmq_connection.get_channel() is None
```

### test_get_channel_connected
Verifies that the `get_channel` method returns

 a valid channel when a connection is established.
```python
def test_get_channel_connected(rabbitmq_connection):
    channel_mock = MagicMock()
    connection_mock = MagicMock(BlockingConnection)
    connection_mock.channel.return_value = channel_mock

    rabbitmq_connection.connection = connection_mock

    channel = rabbitmq_connection.get_channel()

    assert channel is not None
    assert channel is channel_mock
    connection_mock.channel.assert_called_once()
```

## Conclusion
By writing comprehensive test cases using pytest, we can ensure the proper functionality of the `RabbitMQConnection` class. Each test case focuses on a specific aspect of the class, covering scenarios such as successful and failed connections, checking connection status, closing the connection, and obtaining channels.

Through the use of patching and mocking, we can isolate the class under test and simulate different scenarios without relying on real connections. This allows for efficient and reliable testing.

By running these test cases with pytest, you can gain confidence in the correctness and robustness of your `RabbitMQConnection` implementation, ensuring that your RabbitMQ connections are established and managed properly.

Happy testing!