RUDPClient/openspec/changes/archive/2026-04-06-add-jitter-regression-coverage/design.md

Context

Step 5 adds regression tests for the client prediction jitter path. Tests are placed in SyncStrategyTests.cs alongside existing prediction tests, following the same Arrange-Act-Assert pattern using Unity GameObject + Rigidbody + MovementComponent setup.

Goals / Non-Goals

Goals:

• Test that live prediction and replay produce identical trajectories for non-zero turn input (the client-prediction-replay spec requires this).
• Test that ClientPredictionBuffer correctly exposes LastAcknowledgedMoveTick (the client-prediction-diagnostics spec requires this).
• Test that correction magnitude handlers receive valid values from ControlledPlayerCorrection.Resolve.

Non-Goals:

• No production code changes.
• No new specs — existing specs already define the requirements.

Tests to Add

Test 1: Replay trajectory matches live prediction for non-zero turn

ReplayPendingInputs_NonZeroTurn_MatchesLivePrediction

• Arrange: set up MovementComponent, turn=0.5, throttle=1, total duration=0.10s
• Act: run live step-by-step (ApplyTankMovement × 2 × 0.05s) vs replay (ReplayPendingInputs)
• Assert: positions and headings match within tolerance

Test 2: ClientPredictionBuffer exposes LastAcknowledgedMoveTick

ClientPredictionBuffer_LastAcknowledgedMoveTick_IsExposed

• Arrange: buffer with recorded inputs at ticks 10, 11, 12
• Act: apply authoritative state acknowledging tick 11
• Assert: LastAcknowledgedMoveTick == 11

Test 3: Correction magnitude propagates through Reconcile

ControlledPlayerCorrection_CorrectionMagnitude_IsComputable

• Arrange: predicted pose (0,0,0), authoritative (0.5,0,0), 10° heading diff
• Act: ControlledPlayerCorrection.Resolve(...)
• Assert: result.PositionError > 0, result.RotationErrorDegrees > 0