Add edge case tests for empty/None/zero/negative inputs

[Copilot]

What does this changes

Adds 40 edge case test assertions across core, compact, and extra test suites. Tests now validate behavior for empty collections, None values, zero, negative numbers, and boundary conditions.

Core tests (test_util.py):

• collate(): empty list, single item, reverse parameter
• rank(): empty input, all stopwords, exclude_stopwords variations
• find_keyword(): empty list, min_len boundaries (0, 1, 10)
• bahttext(): negative values, large numbers, float precision
• thai_keyboard_dist(): identical chars, None inputs

Compact tests (testc_util.py, testc_tools.py):

• spell_word(): None and empty string
• misspell(): empty string, single char, None handling

Extra tests (testx_util.py, testx_classify.py):

• thai_word_tone_detector(): None and empty string
• GzipModel.predict(): empty input, k parameter variations

What was wrong

Test coverage lacked validation for edge cases: empty collections, None values, zero, negative numbers, and parameter boundaries.

How this fixes it

Documents actual function behavior at boundaries. Tests verify functions handle edge cases correctly or raise appropriate exceptions (TypeError, ValueError, AttributeError).

Your checklist for this pull request

• Passed code styles and structures
• Passed code linting checks and unit test

Original prompt

Gradually add test to increase cover coverage. Focus on tests that check different types of output, including empty collection/iterable, zero, negative, None, as appropriate.

Start first with test (core), testc (compact), then expand to testx (extra)

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud