What will you do if there are no tests in the project and the client refuses to invest time and resources in their development?

In such a situation, when it is not possible to implement comprehensive test coverage, I would focus on the following steps to minimize risks and improve quality:

• Manual testing of key scenarios: Identify the most critical functionalities and perform manual regression testing after each significant change.
• Code quality improvement: Implement static code analyzers (e.g., flake8, Pylint) and linters (e.g., Black, Isort) to maintain a consistent style and detect potential issues.
• Code Review: Actively participate in code review processes to identify logical errors, potential bugs, and improve code readability.
• Logging and monitoring: Set up a logging system to track errors and exceptions in production, as well as implement basic performance monitoring.
• Micro-tests (if possible): If time and module complexity allow, locally write small tests for critical functions, even if they are not integrated into CI/CD.
• Documentation: Provide detailed documentation of system functionalities and expected behaviors to facilitate understanding and debugging.
• Gradual implementation: At any convenient opportunity, such as fixing a critical bug, suggest writing a minimal test that covers the fixed scenario, arguing that it prevents recurrence of errors.

# Example of using a static analyzer
# flake8 --ignore=E501 your_module.py

# Example of using a linter
# black your_module.py

This approach can at least partially compensate for the lack of full testing and reduce the number of defects, even without direct investment in test development.