Add unit tests for email sender

[PulinduVR]

Summary

• This PR contains unit tests added to email_sender.

Checklist

• Documentation or README updated (if behavior/configuration changed)
• Tests added or updated as appropriate
• No breaking changes introduced, or breaking changes clearly documented
• Database migrations applied (if applicable)
• Secrets and configuration handled securely (no secrets committed)
• Formatting, linting, and type checks passed (pre-commit)
• Tests ran locally and verified

Screenshots

Screenshots of the API documentation (swagger) or other relevant artifacts associated with this PR (if applicable).

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
app/core/tests
test_email_sender.py
app/fixtures
email_factory.py
Project Total

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