test: add scheduler integration tests

tests/test_scheduler.rs

@@ -0,0 +1,61 @@
+/// Integration tests for the scheduled tasks (cron) system.
+/// Run with: cargo test --test test_scheduler
+use serde_json::json;
+
+/// Verify that Schedule types (de)serialize correctly.
+#[tokio::test]
+async fn test_scheduler_types_roundtrip() {
+    use picobot::scheduler::Schedule;
+
+    let s1 = Schedule::Every { every_ms: 3600000 };
+    let json = serde_json::to_string(&s1).unwrap();
+    let s2: Schedule = serde_json::from_str(&json).unwrap();
+    match s2 {
+        Schedule::Every { every_ms } => assert_eq!(every_ms, 3600000),
+        _ => panic!("expected Every"),
+    }
+
+    let s1 = Schedule::At { at: 1000000 };
+    let json = serde_json::to_string(&s1).unwrap();
+    let s2: Schedule = serde_json::from_str(&json).unwrap();
+    match s2 {
+        Schedule::At { at } => assert_eq!(at, 1000000),
+        _ => panic!("expected At"),
+    }
+
+    let s1 = Schedule::Cron {
+        expr: "0 0 9 * * *".into(),
+        tz: None,
+    };
+    let json = serde_json::to_string(&s1).unwrap();
+    let s2: Schedule = serde_json::from_str(&json).unwrap();
+    match s2 {
+        Schedule::Cron { expr, tz } => {
+            assert_eq!(expr, "0 0 9 * * *");
+            assert!(tz.is_none());
+        }
+        _ => panic!("expected Cron"),
+    }
+}
+
+/// Verify that next_run_for_schedule produces valid future timestamps.
+#[test]
+fn test_next_run_always_future() {
+    use picobot::scheduler::{next_run_for_schedule, Schedule};
+
+    let now = 1700000000000_i64;
+
+    let schedules = vec![
+        Schedule::Every { every_ms: 60000 },
+        Schedule::Cron {
+            expr: "0 0 9 * * *".into(),
+            tz: None,
+        },
+    ];
+
+    for s in &schedules {
+        let next = next_run_for_schedule(s, now);
+        assert!(next.is_some(), "expected next run for {:?}", s);
+        assert!(next.unwrap() > now, "next run should be after now for {:?}", s);
+    }
+}