[Enhancement] Add edge-case test coverage for validation helper functions

[jyotish6699]

Summary

The validation helper utilities currently have a solid test suite, but several input-handling branches and edge cases are not covered by automated tests.

Proposed Improvements

Add test coverage for the following scenarios:

get_choice()

• Verify custom error_invalid messages are displayed correctly.

get_yes_no()

• Verify behavior when the user enters an empty value before providing valid input.

get_int_list()

• Verify handling of empty input before valid integer list input.

get_float_list()

• Verify handling of empty input before valid float list input.

get_non_empty_string()

• Verify whitespace-only input is treated as empty input.

Benefits

• Improves overall test coverage.
• Validates existing input-validation branches.
• Helps prevent regressions in user input handling.
• Requires no changes to production code.

Verification

The proposed tests have been implemented and verified locally.

• All existing tests pass.
• Full test suite passes successfully (236 passed).

[github-actions]

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