[Test] Add Multiple Tag Deduplication Test Case to Tasks Validation Test Suite

• Labels: good first issue, testing, difficulty:beginner, area:core
• Target File: tests/tasks-validation.test.ts
• Estimated Time: 10–15 minutes
• Difficulty: Level 2 (Beginner)

Why This Matters

Task tagging and filter utilities must ensure duplicate tag arrays (e.g., ['deep-work', 'deep-work', 'urgent']) are deduplicated cleanly so UI task cards do not render duplicate tag badges.

Current Behavior

tests/tasks-validation.test.ts tests general task validation rules, but does not explicitly test array deduplication logic for duplicate tag inputs.

Requested Change

Add a unit test case in tests/tasks-validation.test.ts asserting that task tag array processing returns deduplicated array elements (['deep-work', 'urgent']).

Acceptance Criteria

• Tag array deduplication test case added to tests/tasks-validation.test.ts.
• Test suite executes cleanly: npm run test:file -- tests/tasks-validation.test.ts.

Verification

npm run test:file -- tests/tasks-validation.test.ts

Contributor Notes

Single test case addition.

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Open tests/tasks-validation.test.ts and review the existing task validation tests and tag-processing assertions. Add a test for duplicate tags such as ['deep-work', 'deep-work', 'urgent'] and verify the result is ['deep-work', 'urgent']. Run npm run test:file -- tests/tasks-validation.test.ts; done means the suite passes with the new deduplication case.