[FEATURE]: Build comprehensive regression test suite for attendance calculations & prediction engine

[Hanu2908]

Description

ClassHub relies on exact integer arithmetic (target * total - 100 * attended) / (100 - target) in src/lib/utils/attendance.ts to calculate attendance metrics, safe bunks, and required classes without floating-point IEEE 754 precision issues.

To ensure future enhancements (such as configurable attendance targets and academic calendar integrations) do not cause mathematical regressions, we need a dedicated, comprehensive regression test suite covering the entire calculation and prediction engine across multiple target thresholds.

Relevant files

• src/lib/utils/attendance.ts (Core attendance formulas, safe bunk calculations, boost/bunk simulator)
• src/lib/utils/attendancePrediction.ts (Recovery projection engine with timetable frequency & academic calendar linkage)
• tests/unit/attendanceCalculations.test.ts (Existing unit test suite)

Requirements and acceptance criteria

1. Threshold variation coverage:

   • Verify calculation correctness across standard target percentages: 75%, 80%, 85%, and 90%.
   • Verify integer rounding behavior for safe bunks (Math.floor) and required classes (Math.ceil).

2. Boundary and edge case matrix:

   • 0 attended / 0 held (Initial state: should return 0% without NaN or division by zero).
   • 100% attendance (e.g. 20/20: safe bunk calculation must return exact positive integer).
   • 0% attendance (e.g. 0/10: required classes calculation must return exact number needed to recover).
   • Exact threshold match (e.g. 15/20 = 75%: safe bunk = 0, needed = 0).
   • Single class away from threshold (boundary transitions).

3. Simulator and recovery prediction assertions:

   • Verify simulateBoost(current, additionalAttended) and simulateBunk(current, additionalMissed).
   • Verify calculateAttendancePrediction projects recovery dates based on subject timetable frequencies and institutional break dates.

4. Testing framework:

   • Add new test cases to tests/unit/attendanceCalculations.test.ts using Vitest (describe, it, expect).
   • All tests must pass with npm test.

Testing locally

npm test tests/unit/attendanceCalculations.test.ts