Unittest File created for MTA- STS

[vijaykannan21]

:eyes: Purpose

•The set of unit tests for a function that checks the MTA-STS (Mail Transfer Agent Strict Transport Security) configurations kept in AWS S3 buckets for a list of domains is defined by the provided code. These tests are primarily used to verify that the function operates as intended in various contexts. These cases cover handling the lack of AWS credentials and retrieving MTA-STS configurations both successfully and unsuccessfully with the'mode: enforce' directive. To mimic various answers from the S3 service, the tests make use of the unittest.mock library and the unittest framework.

:recycle: What's Changed

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:memo: Notes

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:white_check_mark: Things to Check (Optional)

• [ ] I have run all unit tests, and they pass.
• [ ] I have ensured my code follows the project's coding standards.
• [ ] I have checked that all new dependencies are up to date and necessary.

[github-actions[bot]]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
❌ PYTHON	flake8	2		2	0.48s
✅ PYTHON	isort	2	1	0	0.33s
❌ PYTHON	pylint	2		5	2.23s
✅ REPOSITORY	gitleaks	yes		no	1.39s

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[jasonBirchall]

@vijaykannan21 can you make this a draft until it's ready to review?