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Testing.md

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+# Testing
+
+🌐 **English** · [Dansk](Testing-da) · [Bahasa Melayu](Testing-ms)
+
+```bash
+python -m pytest
+```
+
+![The test run](https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/032-birthday-wisher/raw/branch/main/docs/images/tests.png)
+
+The tests use a fake SMTP connection and temporary files. They need no network, no `.env` and no credentials. Optional checks:
+
+```bash
+python -m ruff check src tests
+python -m mypy src tests
+```
+
+API documentation from the Doxygen comments: `doxygen Doxyfile` (output in `docs/doxygen/`).