如何为moto未实现的EC2 describe_reserved_instances编写单元测试

方案一：直接Mock EC2客户端方法 #

无需依赖moto的未实现功能，用Python标准库的unittest.mock（或pytest-mock）模拟describe_reserved_instances的返回值，快速完成单元测试，聚焦业务逻辑验证。

基于unittest的示例代码 #

import unittest
from unittest.mock import Mock
from your_module import get_reserved_instance  # 替换为实际模块名

class TestGetReservedInstance(unittest.TestCase):
    def test_get_reserved_instance(self):
        # 构造模拟返回数据
        mock_ri_response = {
            "ReservedInstances": [
                {
                    "ReservedInstancesId": "ri-12345678",
                    "InstanceType": "t2.micro",
                    "OfferingClass": "convertible"
                }
            ]
        }
        
        # 创建Mock的EC2客户端
        mock_ec2_client = Mock()
        mock_ec2_client.describe_reserved_instances.return_value = mock_ri_response
        
        # 调用被测试函数
        result = get_reserved_instance(mock_ec2_client)
        
        # 验证结果
        self.assertEqual(len(result), 1)
        self.assertEqual(result[0]["OfferingClass"], "convertible")
        
        # 验证方法调用参数是否匹配
        mock_ec2_client.describe_reserved_instances.assert_called_once_with(
            Filters=[],
            OfferingClass="convertible"
        )

if __name__ == "__main__":
    unittest.main()

基于pytest的示例代码 #

from unittest.mock import Mock
from your_module import get_reserved_instance

def test_get_reserved_instance():
    mock_ri_response = {
        "ReservedInstances": [
            {"ReservedInstancesId": "ri-12345678", "OfferingClass": "convertible"}
        ]
    }
    mock_ec2_client = Mock()
    mock_ec2_client.describe_reserved_instances.return_value = mock_ri_response
    
    result = get_reserved_instance(mock_ec2_client)
    
    assert len(result) == 1
    assert result[0]["OfferingClass"] == "convertible"
    mock_ec2_client.describe_reserved_instances.assert_called_once_with(
        Filters=[],
        OfferingClass="convertible"
    )

方案二：扩展moto的MockEC2类实现缺失方法 #

如果需要贴近真实AWS环境的测试（比如结合moto已实现的其他功能），可以扩展moto的MockEC2类，补充describe_reserved_instances的实现。

示例代码 #

import pytest
from moto.ec2.models import MockEC2
from moto import mock_ec2
from your_module import get_reserved_instance
import boto3

# 扩展MockEC2类，添加describe_reserved_instances方法
class MockEC2WithRI(MockEC2):
    def describe_reserved_instances(self, Filters=None, OfferingClass=None, **kwargs):
        # 模拟真实AWS的返回逻辑
        reserved_instances = []
        if OfferingClass == "convertible":
            reserved_instances = [
                {
                    "ReservedInstancesId": "ri-87654321",
                    "InstanceType": "t3.small",
                    "OfferingClass": "convertible"
                }
            ]
        return {"ReservedInstances": reserved_instances}

@mock_ec2
def test_get_reserved_instance_with_extended_moto():
    ec2_client = boto3.client("ec2", region_name="us-east-1")
    
    # 替换底层的mock实例为自定义实现
    ec2_client._endpoint._instance = MockEC2WithRI()
    
    # 调用被测试函数
    result = get_reserved_instance(ec2_client)
    
    # 验证结果
    assert len(result) == 1
    assert result[0]["OfferingClass"] == "convertible"

方案对比 #

• 方案一：实现简单，专注业务逻辑测试，无需关注moto细节，适合纯单元测试场景。
• 方案二：更贴近真实AWS交互，适合需要结合其他moto已实现服务的集成测试，但实现复杂度更高。

内容的提问来源于stack exchange，提问作者Jason LiLy