Add tests (97% coverage), fix pagination bug, document 5 remaining bugs, implement /assign endpointFeature/tests bugfix assign

[tusharsach16]

Summary

Added unit and integration tests for the Task Manager API, identified and documented 6 bugs, fixed one, and implemented the PATCH /tasks/:id/assign endpoint.

Tests

• 63 tests across 2 test files (29 unit, 34 integration)
• 97.4% statement coverage, 95.3% branch coverage
• Unit tests cover every exported function in taskService.js directly
• Integration tests hit all 7 endpoints via Supertest, including validation edge cases
• Tests that demonstrate unfixed bugs assert the current (buggy) behavior and are annotated with comments explaining the issue

Bug Fixed

Pagination off-by-one (taskService.js:12): getPaginated calculated the offset as page * limit instead of (page - 1) * limit, causing page 1 to skip all its results. One-line fix.

Bugs Documented (BUGS.md)

5 additional bugs identified and documented with expected/actual behavior, root cause, and proposed fix:

1. getByStatus uses .includes() instead of === — partial strings like "do" match both "todo" and "done"
2. completeTask() hardcodes priority: 'medium', overwriting the task's original priority
3. Validators use truthiness checks (if (body.status)) — empty string "" bypasses enum validation
4. GET /tasks has mutually exclusive branches for status filtering and pagination — combining both ignores pagination
5. update() spreads all client fields without stripping id or createdAt — a PUT request can overwrite internal metadata

New Endpoint

PATCH /tasks/:id/assign — assigns a user to a task.

• Body: { "assignee": "string" } (required, non-empty)
• Returns the full updated task object (200)
• 404 if task doesn't exist, 400 if assignee is missing/empty/non-string
• Reassignment is allowed (overwrites previous assignee)
• Does not change task status
• Validation in validateAssignTask(), consistent with existing validator pattern
• assignee: null added to create() for consistent task shape