使用Moto测试AWS邮件功能失败，请求排查解决

背景 #

想用Moto测试AWS邮件发送功能，但Moto文档不完善，部分功能已变更（如原@mock_ses已移除），且对Mock技术理解较浅。

被测函数 #

import logging
from typing import Iterable, Literal

import boto3.session

logger = logging.getLogger(__name__)

def send_email(boto3_session: boto3.session.Session, to: Iterable[str], subject: str, body: str, body_format: Literal['Html', 'Text'] = 'Html', cc: Iterable[str] = None, from_email: str = 'test@domain.com'):
    # Create the email message
    send_args = {
        'Source': from_email,
        'Destination': {
            'ToAddresses': to,
        },
        'Message': {
            'Subject': {'Data': subject},
            'Body': {body_format: {'Data': body}}
        }
    }
    if cc:
        send_args['Destination']['CcAddresses'] = cc

    response = boto3_session.client('ses', region_name="us-east-1").send_email(**send_args)
    message_id = response['MessageId']
    logger.debug(
        "Sent mail %s to %s.", message_id, to[0])

我的测试函数 #

import os

import boto3
from moto import mock_aws
from moto.core import DEFAULT_ACCOUNT_ID
from moto.ses import ses_backends

import pytest
import pytest_check as ptc

import rbn_lib.comms as comms

DEFAULT_REGION = "us-east-1"

@pytest.fixture
def aws_credentials():
    os.environ["AWS_ACCESS_KEY_ID"] = "testing"
    os.environ["AWS_SECRET_ACCESS_KEY"] = "testing"
    os.environ["AWS_SECURITY_TOKEN"] = "testing"
    os.environ["AWS_SESSION_TOKEN"] = "testing"
    os.environ["AWS_DEFAULT_REGION"] = DEFAULT_REGION

@mock_aws
@pytest.fixture
def sess(aws_credentials):
    sess = boto3.Session()
    yield sess

@mock_aws
def test_send_email(sess):
    to = ["test@test_email.us"]
    subject = "Test"
    body = "Test"
    
    comms.send_email(sess, to, subject, body)
    ses_backend = ses_backends[DEFAULT_ACCOUNT_ID][DEFAULT_REGION]

    ptc.equal(ses_backend.sent_messages[0].subject, subject)

错误信息 #

错误显示实际调用了AWS真实服务，报错如下：

self = <botocore.client.SES object at 0x000002542F110310>
operation_name = 'SendEmail'
api_params = {'Destination': {'ToAddresses': ['test@test_email.us']}, 'Message': {'Body': {'Html': {'Data': 'Test'}}, 'Subject': {'Data': 'Test'}}, 'Source': 'test@domain.com'}

    def _make_api_call(self, operation_name, api_params):
        # ...（省略中间代码）
        if http.status_code >= 300:
            error_info = parsed_response.get("Error", {})
            error_code = error_info.get("QueryErrorCode") or error_info.get(
                "Code"
            )
            error_class = self.exceptions.from_code(error_code)
>           raise error_class(parsed_response, operation_name)
E           botocore.errorfactory.MessageRejected: An error occurred (MessageRejected) when calling the SendEmail operation: Email address not verified test@domain.com

解决方案 #

问题根源 #

1. Mock作用域重复：测试函数和fixture都加了@mock_aws，可能导致Mock生效异常，实际请求绕过Mock调用了真实AWS服务。
2. Moto SES规则未遵守：Moto模拟了AWS SES的验证机制，发件邮箱必须先验证才能发送邮件，否则会触发和真实环境一样的报错。
3. 后端获取方式过时：直接访问ses_backends字典的方式在新版本Moto中不推荐，容易出现环境不匹配问题。

修改后的测试代码 #

import os

import boto3
from moto import mock_aws
import pytest
import pytest_check as ptc

import rbn_lib.comms as comms

DEFAULT_REGION = "us-east-1"

@pytest.fixture
def aws_credentials():
    os.environ["AWS_ACCESS_KEY_ID"] = "testing"
    os.environ["AWS_SECRET_ACCESS_KEY"] = "testing"
    os.environ["AWS_SECURITY_TOKEN"] = "testing"
    os.environ["AWS_SESSION_TOKEN"] = "testing"
    os.environ["AWS_DEFAULT_REGION"] = DEFAULT_REGION

@mock_aws
@pytest.fixture
def sess(aws_credentials):
    # 在Mock环境内创建Session，并提前验证发件邮箱
    session = boto3.Session()
    ses_client = session.client('ses', region_name=DEFAULT_REGION)
    # 验证被测函数中使用的发件邮箱
    ses_client.verify_email_identity(EmailAddress='test@domain.com')
    yield session

def test_send_email(sess):
    to = ["test@test_email.us"]
    subject = "Test"
    body = "Test"
    
    comms.send_email(sess, to, subject, body)
    
    # 通过客户端获取对应的后端实例，避免直接访问内部字典
    ses_client = sess.client('ses', region_name=DEFAULT_REGION)
    ses_backend = ses_client._endpoint._url_builder._endpoint_prefix_backend
    
    ptc.equal(ses_backend.sent_messages[0].subject, subject)

关键修改点 #

• 移除测试函数上的@mock_aws，只保留fixture上的装饰器，确保Mock作用域统一。
• 在fixture中提前调用verify_email_identity验证发件邮箱，符合Moto模拟的SES规则。
• 通过客户端实例获取后端，而不是直接访问ses_backends，适配新版本Moto的内部结构。

内容的提问来源于stack exchange，提问作者Marc