test(tui-core): add unit tests for UiState state machine (#2450)

Add 25 unit tests covering the previously untested UiState::reduce
state machine and snapshot:

- Default state verification
- Key navigation: pane switching (1-5), unknown key no-op
- Prompt lifecycle: pending_tasks increment, response delta tracking
- Tool lifecycle: active_tool set/clear, pending_tasks decrement, saturation
- Job lifecycle: active_jobs increment/decrement, progress clamping, saturation
- Approval lifecycle: pending_approvals increment/decrement, saturation
- Pause/Resume: flag toggling
- Tick: ScheduleBackgroundRefresh effect
- Snapshot: field presence, state change reflection

Co-authored-by: Hu Qiantao <huqiantao@HudeMacBook-Air.local>

crates/tui-core/src/lib.rs

@@ -227,3 +227,244 @@ impl UiState {
         )
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── Default state ──────────────────────────────────────────────────
+
+    #[test]
+    fn default_state_is_chat_pane_and_ready() {
+        let state = UiState::default();
+        assert_eq!(state.active_pane, Pane::Chat);
+        assert!(!state.paused);
+        assert_eq!(state.last_response_delta, None);
+        assert_eq!(state.active_tool, None);
+        assert_eq!(state.pending_tasks, 0);
+        assert_eq!(state.active_jobs, 0);
+        assert_eq!(state.pending_approvals, 0);
+        assert_eq!(state.status_line, "ready");
+    }
+
+    // ── Key navigation ─────────────────────────────────────────────────
+
+    #[test]
+    fn key_1_switches_to_chat_pane() {
+        let mut state = UiState::default();
+        let effects = state.reduce(UiEvent::KeyPressed('1'));
+        assert_eq!(state.active_pane, Pane::Chat);
+        assert_eq!(effects, vec![UiEffect::Render]);
+    }
+
+    #[test]
+    fn key_2_switches_to_diff_pane() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::KeyPressed('2'));
+        assert_eq!(state.active_pane, Pane::Diff);
+    }
+
+    #[test]
+    fn key_3_switches_to_tasks_pane() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::KeyPressed('3'));
+        assert_eq!(state.active_pane, Pane::Tasks);
+    }
+
+    #[test]
+    fn key_4_switches_to_agents_pane() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::KeyPressed('4'));
+        assert_eq!(state.active_pane, Pane::Agents);
+    }
+
+    #[test]
+    fn key_5_switches_to_jobs_pane() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::KeyPressed('5'));
+        assert_eq!(state.active_pane, Pane::Jobs);
+    }
+
+    #[test]
+    fn unknown_key_produces_no_effects() {
+        let mut state = UiState::default();
+        let effects = state.reduce(UiEvent::KeyPressed('x'));
+        assert!(effects.is_empty());
+        assert_eq!(state.active_pane, Pane::Chat);
+    }
+
+    // ── Prompt lifecycle ───────────────────────────────────────────────
+
+    #[test]
+    fn prompt_submitted_increments_pending_tasks() {
+        let mut state = UiState::default();
+        let effects = state.reduce(UiEvent::PromptSubmitted("hello".to_string()));
+        assert_eq!(state.pending_tasks, 1);
+        assert_eq!(state.status_line, "prompt submitted");
+        assert!(effects.contains(&UiEffect::Render));
+        assert!(effects.contains(&UiEffect::PersistCheckpoint));
+    }
+
+    #[test]
+    fn response_delta_updates_last_delta() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ResponseDelta("partial".to_string()));
+        assert_eq!(state.last_response_delta, Some("partial".to_string()));
+        assert_eq!(state.status_line, "streaming response");
+    }
+
+    // ── Tool lifecycle ─────────────────────────────────────────────────
+
+    #[test]
+    fn tool_started_sets_active_tool() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ToolStarted("shell".to_string()));
+        assert_eq!(state.active_tool, Some("shell".to_string()));
+        assert_eq!(state.status_line, "tool running: shell");
+    }
+
+    #[test]
+    fn tool_finished_clears_active_tool_and_decrements_tasks() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::PromptSubmitted("test".to_string()));
+        assert_eq!(state.pending_tasks, 1);
+        state.reduce(UiEvent::ToolFinished("shell".to_string()));
+        assert_eq!(state.active_tool, None);
+        assert_eq!(state.pending_tasks, 0);
+        assert_eq!(state.status_line, "tool finished: shell");
+    }
+
+    #[test]
+    fn tool_finished_saturates_at_zero() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ToolFinished("shell".to_string()));
+        assert_eq!(state.pending_tasks, 0);
+    }
+
+    // ── Job lifecycle ──────────────────────────────────────────────────
+
+    #[test]
+    fn job_queued_increments_active_jobs() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::JobQueued("build".to_string()));
+        assert_eq!(state.active_jobs, 1);
+        assert_eq!(state.status_line, "job queued");
+    }
+
+    #[test]
+    fn job_progress_updates_status_line() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::JobProgress {
+            job_id: "j1".to_string(),
+            progress: 75,
+        });
+        assert_eq!(state.status_line, "job progress: 75%");
+    }
+
+    #[test]
+    fn job_progress_clamps_over_100() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::JobProgress {
+            job_id: "j1".to_string(),
+            progress: 150,
+        });
+        assert_eq!(state.status_line, "job progress: 100%");
+    }
+
+    #[test]
+    fn job_completed_decrements_active_jobs() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::JobQueued("build".to_string()));
+        assert_eq!(state.active_jobs, 1);
+        state.reduce(UiEvent::JobCompleted("build".to_string()));
+        assert_eq!(state.active_jobs, 0);
+        assert_eq!(state.status_line, "job completed");
+    }
+
+    #[test]
+    fn job_completed_saturates_at_zero() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::JobCompleted("build".to_string()));
+        assert_eq!(state.active_jobs, 0);
+    }
+
+    // ── Approval lifecycle ─────────────────────────────────────────────
+
+    #[test]
+    fn approval_requested_increments_pending() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ApprovalRequested("exec".to_string()));
+        assert_eq!(state.pending_approvals, 1);
+        assert_eq!(state.status_line, "approval requested");
+    }
+
+    #[test]
+    fn approval_resolved_decrements_pending() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ApprovalRequested("exec".to_string()));
+        state.reduce(UiEvent::ApprovalResolved("exec".to_string()));
+        assert_eq!(state.pending_approvals, 0);
+        assert_eq!(state.status_line, "approval resolved");
+    }
+
+    #[test]
+    fn approval_resolved_saturates_at_zero() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::ApprovalResolved("exec".to_string()));
+        assert_eq!(state.pending_approvals, 0);
+    }
+
+    // ── Pause/Resume ───────────────────────────────────────────────────
+
+    #[test]
+    fn pause_sets_paused_flag() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::PauseRequested);
+        assert!(state.paused);
+        assert_eq!(state.status_line, "paused");
+    }
+
+    #[test]
+    fn resume_clears_paused_flag() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::PauseRequested);
+        state.reduce(UiEvent::ResumeRequested);
+        assert!(!state.paused);
+        assert_eq!(state.status_line, "resumed");
+    }
+
+    // ── Tick ────────────────────────────────────────────────────────────
+
+    #[test]
+    fn tick_schedules_background_refresh() {
+        let mut state = UiState::default();
+        let effects = state.reduce(UiEvent::Tick);
+        assert_eq!(effects, vec![UiEffect::ScheduleBackgroundRefresh]);
+    }
+
+    // ── Snapshot ────────────────────────────────────────────────────────
+
+    #[test]
+    fn snapshot_contains_all_fields() {
+        let state = UiState::default();
+        let snap = state.snapshot();
+        assert!(snap.contains("pane=Chat"));
+        assert!(snap.contains("paused=false"));
+        assert!(snap.contains("pending_tasks=0"));
+        assert!(snap.contains("active_jobs=0"));
+        assert!(snap.contains("pending_approvals=0"));
+        assert!(snap.contains("status=ready"));
+    }
+
+    #[test]
+    fn snapshot_reflects_state_changes() {
+        let mut state = UiState::default();
+        state.reduce(UiEvent::KeyPressed('2'));
+        state.reduce(UiEvent::PauseRequested);
+        state.reduce(UiEvent::PromptSubmitted("test".to_string()));
+        let snap = state.snapshot();
+        assert!(snap.contains("pane=Diff"));
+        assert!(snap.contains("paused=true"));
+        assert!(snap.contains("pending_tasks=1"));
+    }
+}