Isolate test environments

Tests should be isolated from the production environment to prevent side effects and ensure reproducibility. This principle has two main applications:

1. Use proper temporary files: Instead of writing test files to the current directory where they might overwrite real files, use the tempfile module to create isolated test files.

2. Establish correct directory context: Ensure tests run in the appropriate directory context to prevent location-dependent failures.

Example:

# Good: Use temporary files instead of hardcoded paths
import tempfile
message_file_path = tempfile.mktemp()
main(["--message-file", message_file_path], input=DummyInput(), output=DummyOutput())

# Good: Explicitly set the directory context for tests
with change_dir(testdir):
    # Test code runs in the correct context
    # ...

Following these practices prevents tests from accidentally modifying real files and ensures they’ll run consistently regardless of the current working directory.