feat: tested, fixed bugs and added new PATCH /tasks/:id/assign end point

[redstonenight347-oss]

Pull Request: Comprehensive Test Suite, Bug Fixes & PATCH /tasks/:id/assign Feature

📌 Summary of Changes

This PR delivers a comprehensive test suite (108 tests with >96% coverage), resolves critical bug fixes across the core API, and implements the PATCH /tasks/:id/assign endpoint with full validation and test coverage.

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🚀 Key Improvements

1. Test Suite & Coverage (Day 1 Requirements)

• Unit Tests (tests/taskService.test.js): 53 unit tests covering all functions in taskService.js.
• Integration Tests (tests/tasks.test.js): 55 integration tests using supertest covering all API routes, edge cases, status validations, and failure modes.
• Coverage Summary:
  • src/routes/tasks.js: 100%
  • src/services/taskService.js: 100% lines / 95% branch
  • src/utils/validators.js: 96.77%
  • Total Suite: 108 tests passing, 0 failing.

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2. Bug Fixes (Day 2 Part A & B)

• 🐛 Pagination Off-by-One Fix:
  • Updated getPaginated offset formula from page * limit to (page - 1) * limit. Page 1 now correctly returns items starting from index 0. Added fallback guards for negative/invalid page & limit values.
• 🐛 Exact Status Matching Fix:
  • Replaced t.status.includes(status) substring matching with exact equality t.status === status in getByStatus.
• 🐛 Priority Clobbering Fix on Task Completion:
  • Removed hardcoded priority: 'medium' overwrite inside completeTask, preserving the task's original priority (low/medium/high).
• 🐛 Immutable Fields Protection in PUT:
  • Destructured and stripped protected fields (id, createdAt, completedAt) in update() so client request bodies cannot alter system-managed identifiers or timestamps.
• 🐛 Query Parameter Validation:
  • Implemented validateGetTask in validators.js to return 400 Bad Request when filtering with an invalid status parameter (e.g., ?status=banana).

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3. New Feature: PATCH /tasks/:id/assign (Day 2 Part C)

Implemented task assignment capabilities:

• Route: PATCH /tasks/:id/assign
• Body: { "assignee": "string" }
• Behavior:
  • Validates assignee is a non-empty, non-whitespace string (returns 400 Bad Request otherwise).
  • Updates the task in the in-memory store and returns the full updated task object with 200 OK.
  • Returns 404 Not Found if the task ID does not exist.
  • Supports re-assigning existing tasks.
  • Updated task schema constructor to initialize assignee: null by default.

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🧪 Verification & Test Results

npm run coverage

-----------------|---------|----------|---------|---------|-------------------
File             | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-----------------|---------|----------|---------|---------|-------------------
All files        |   96.95 |    95.69 |   93.54 |   96.66 |
 src             |   69.23 |       75 |       0 |   69.23 |
  app.js         |   69.23 |       75 |       0 |   69.23 | 10-11,17-18
 src/routes      |     100 |      100 |     100 |     100 |
  tasks.js       |     100 |      100 |     100 |     100 |
 src/services    |     100 |       95 |     100 |     100 |
  taskService.js |     100 |       95 |     100 |     100 | 23
 src/utils       |   96.77 |    95.34 |     100 |   96.77 |
  validators.js  |   96.77 |    95.34 |     100 |   96.77 | 31
-----------------|---------|----------|---------|---------|-------------------
Test Suites: 2 passed, 2 total
Tests:       108 passed, 108 total
Snapshots:   0 total
Time:        2.939 s

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📝 Notes for Submission

• Design Decisions: assignee validation strictly checks for non-empty string types after trimming whitespace. Re-assignment is explicitly permitted.
• Future Improvements:
  • Standardize pagination response format to return metadata (total, page, limit, totalPages).
  • Align README.md documentation status values (pending, in-progress, completed) with the active code implementation (todo, in_progress, done).