Explicitly close files to prevent resource leak

[Stephen0512]

What

This pull request fixes a file-handling issue in the tests.

Why

The current implementation uses open() without explicitly closing the file, which can potentially lead to resource leaks. While Python's garbage collector will eventually close the file once it is no longer referenced, it is generally better practice to explicitly close files or use a context manager.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause a breaking change)
• Tests (adds or updates tests)
• Documentation (adds or updates documentation)
• Refactor (style improvements, performance improvements, code refactoring)
• Revert (reverts a commit)
• CI/Build (adds or updates a script, change in external dependencies)

Testing

Rerun the existing test suites.

Checklist

• My code follows the coding conventions
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added new unit tests