From d3c23c71482fd6a946e5ddb0af8b84f45a6862b7 Mon Sep 17 00:00:00 2001
From: Zachery Aaron Shores-Chmielewski <zachanon@gmail.com>
Date: Fri, 6 Feb 2026 21:42:47 +0700
Subject: [PATCH] refactor: better worker thread tests

---
 src/worker/mod.rs   |   2 +-
 src/worker/tests.rs | 882 +++++++++++++++++---------------------------
 2 files changed, 346 insertions(+), 538 deletions(-)

diff --git a/src/worker/mod.rs b/src/worker/mod.rs
index f113ba6..493b9c4 100644
--- a/src/worker/mod.rs
+++ b/src/worker/mod.rs
@@ -274,7 +274,7 @@ impl ActorPool {
 
 
 
-pub struct Mailbox<M: Message> {
+pub(crate) struct Mailbox<M: Message> {
     queue: VecDeque<M>,
     waterlevel: usize,
 }
diff --git a/src/worker/tests.rs b/src/worker/tests.rs
index 0048b61..720d968 100644
--- a/src/worker/tests.rs
+++ b/src/worker/tests.rs
@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::collections::HashMap;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::thread;
@@ -7,587 +8,398 @@ use crate::actor::{ActorAddress, AnyActor};
 use crate::address_map::{AddressMap, Placement, WorkerId};
 use crate::channel::Receiver;
 use crate::config::{BackoffPolicy, RuntimeConfig};
-use crate::runtime::{ContextInner, Ctx, Envelope, InboxRegistry};
-use super::{ActorPool, Mailbox, TickContext, Worker, WorkerStats};
-use crate::Error;
+use crate::runtime::{Ctx, Envelope, InboxRegistry};
 
-// ── Test helpers ────────────────────────────────────────────────────
+use super::{TickContext, Worker, WorkerStats};
 
-#[derive(Clone, Debug, PartialEq)]
-struct TestMsg(u64);
+// ── Actors ─────────────────────────────────────────────────────────
 
-/// A minimal actor that counts how many messages it handled.
-struct CounterActor {
-    counter: Arc<AtomicUsize>,
-}
+/// Counts how many u64 messages it successfully handled.
+struct CounterActor(Arc<AtomicUsize>);
 
 impl AnyActor for CounterActor {
     fn handle_any(&mut self, _ctx: &Ctx, msg: Box<dyn Any + Send>) {
         if msg.downcast::<u64>().is_ok() {
-            self.counter.fetch_add(1, Ordering::Relaxed);
+            self.0.fetch_add(1, Ordering::Relaxed);
         }
     }
 }
 
-fn make_test_actor(
-    _addr: ActorAddress,
-) -> (Box<dyn AnyActor>, Arc<AtomicUsize>) {
-    let counter = Arc::new(AtomicUsize::new(0));
-    let actor = CounterActor {
-        counter: counter.clone(),
-    };
-    (Box::new(actor), counter)
-}
+// ── Harness ────────────────────────────────────────────────────────
 
-/// No-op ContextInner for ActorPool tests.
-struct StubContextInner {
-    waterlevel: usize,
-}
-
-impl ContextInner for StubContextInner {
-    fn send_any(&self, _addr: ActorAddress, _msg: Box<dyn Any + Send>) -> Result<(), Error> {
-        Ok(())
-    }
-
-    fn spawn_any(&self, _addr: ActorAddress, _actor: Box<dyn AnyActor>) -> Result<(), Error> {
-        Ok(())
-    }
-
-    fn mailbox_waterlevel(&self) -> usize {
-        self.waterlevel
-    }
-}
-
-fn make_addr(id: u8) -> ActorAddress {
+fn addr(id: u8) -> ActorAddress {
     let mut bytes = [0u8; 32];
     bytes[0] = id;
     ActorAddress(bytes)
 }
 
-// ── Mailbox tests ───────────────────────────────────────────────────
-
-#[test]
-fn mailbox_new_is_empty() {
-    let mb: Mailbox<u64> = Mailbox::new(10);
-    assert_eq!(mb.len(), 0);
-    assert!(mb.is_empty());
+/// Self-contained single-worker test environment.
+///
+/// Holds the worker, its channels, shared state for TickContext, and
+/// per-actor handle counters — everything needed to drive scenarios.
+struct Env {
+    worker: Worker,
+    stats: Arc<WorkerStats>,
+    feed_transfer: crate::channel::Sender<Envelope>,
+    feed_spawn: crate::channel::Sender<(ActorAddress, Box<dyn AnyActor>)>,
+    address_map: AddressMap,
+    placement: Placement,
+    inbox_registry: InboxRegistry,
+    config: RuntimeConfig,
+    tc_transfer_txs: Vec<crate::channel::Sender<Envelope>>,
+    tc_spawn_txs: Vec<crate::channel::Sender<(ActorAddress, Box<dyn AnyActor>)>>,
+    counters: HashMap<u8, Arc<AtomicUsize>>,
 }
 
-#[test]
-fn mailbox_push_increments_len() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    mb.push(1);
-    assert_eq!(mb.len(), 1);
-    mb.push(2);
-    assert_eq!(mb.len(), 2);
-}
-
-#[test]
-fn mailbox_pop_returns_fifo_order() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    mb.push(10);
-    mb.push(20);
-    mb.push(30);
-    assert_eq!(mb.pop(), Some(10));
-    assert_eq!(mb.pop(), Some(20));
-    assert_eq!(mb.pop(), Some(30));
-}
-
-#[test]
-fn mailbox_pop_empty_returns_none() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    assert_eq!(mb.pop(), None);
-}
-
-#[test]
-fn mailbox_pop_drains_to_empty() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    mb.push(1);
-    mb.push(2);
-    mb.pop();
-    mb.pop();
-    assert!(mb.is_empty());
-    assert_eq!(mb.len(), 0);
-}
-
-#[test]
-fn mailbox_push_pop_interleaved() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    mb.push(1);
-    mb.push(2);
-    assert_eq!(mb.pop(), Some(1));
-    mb.push(3);
-    assert_eq!(mb.pop(), Some(2));
-    assert_eq!(mb.pop(), Some(3));
-    assert_eq!(mb.pop(), None);
-}
-
-#[test]
-fn drain_count_empty() {
-    let mb: Mailbox<u64> = Mailbox::new(10);
-    assert_eq!(mb.drain_count(), 0);
-}
-
-#[test]
-fn drain_count_below_waterlevel() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..5 {
-        mb.push(i);
+impl Env {
+    fn new() -> Self {
+        Self::with_config(RuntimeConfig::default())
     }
-    assert_eq!(mb.drain_count(), 5);
-}
 
-#[test]
-fn drain_count_at_waterlevel_minus_one() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..9 {
-        mb.push(i);
+    fn with_config(config: RuntimeConfig) -> Self {
+        let transfer_rx = Receiver::<Envelope>::new(256);
+        let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(256);
+
+        let feed_transfer = transfer_rx.new_sender();
+        let feed_spawn = spawn_rx.new_sender();
+        let tc_transfer = transfer_rx.new_sender();
+        let tc_spawn = spawn_rx.new_sender();
+
+        let stats = Arc::new(WorkerStats::new());
+        let worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, stats.clone());
+
+        Self {
+            worker,
+            stats,
+            feed_transfer,
+            feed_spawn,
+            address_map: AddressMap::new(),
+            placement: Placement::new(1),
+            inbox_registry: InboxRegistry::new(),
+            config,
+            tc_transfer_txs: vec![tc_transfer],
+            tc_spawn_txs: vec![tc_spawn],
+            counters: HashMap::new(),
+        }
     }
-    // len=9 < waterlevel=10 → returns len
-    assert_eq!(mb.drain_count(), 9);
-}
 
-#[test]
-fn drain_count_at_waterlevel() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..10 {
-        mb.push(i);
+    /// Enqueue an actor spawn (drained on next tick, phase 1).
+    fn spawn(&mut self, id: u8) {
+        let counter = Arc::new(AtomicUsize::new(0));
+        let actor: Box<dyn AnyActor> = Box::new(CounterActor(counter.clone()));
+        self.feed_spawn.try_send((addr(id), actor)).ok().unwrap();
+        self.counters.insert(id, counter);
     }
-    // len=10 >= waterlevel=10 → returns len >> 1 = 5
-    assert_eq!(mb.drain_count(), 5);
-}
 
-#[test]
-fn drain_count_at_waterlevel_plus_one() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..11 {
-        mb.push(i);
-    }
-    // len=11 >= waterlevel=10 → returns 11 >> 1 = 5
-    assert_eq!(mb.drain_count(), 5);
-}
-
-#[test]
-fn drain_count_well_above_waterlevel() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..100 {
-        mb.push(i);
-    }
-    // len=100 >= waterlevel=10 → returns 100 >> 1 = 50
-    assert_eq!(mb.drain_count(), 50);
-}
-
-#[test]
-fn drain_count_odd_len_truncates() {
-    let mut mb: Mailbox<u64> = Mailbox::new(1);
-    for i in 0..7 {
-        mb.push(i);
-    }
-    // len=7 >= waterlevel=1 → returns 7 >> 1 = 3
-    assert_eq!(mb.drain_count(), 3);
-}
-
-#[test]
-fn drain_count_waterlevel_one() {
-    let mut mb: Mailbox<u64> = Mailbox::new(1);
-    mb.push(42);
-    // len=1 >= waterlevel=1 → returns 1 >> 1 = 0
-    assert_eq!(mb.drain_count(), 0);
-}
-
-#[test]
-fn drain_count_waterlevel_zero() {
-    // waterlevel=0 means len >= 0 is always true → always half-drain
-    let mb: Mailbox<u64> = Mailbox::new(0);
-    assert_eq!(mb.drain_count(), 0); // empty: 0 >> 1 = 0
-
-    let mut mb2: Mailbox<u64> = Mailbox::new(0);
-    mb2.push(1);
-    // len=1 >= waterlevel=0 → returns 1 >> 1 = 0
-    assert_eq!(mb2.drain_count(), 0);
-
-    let mut mb3: Mailbox<u64> = Mailbox::new(0);
-    mb3.push(1);
-    mb3.push(2);
-    // len=2 >= waterlevel=0 → returns 2 >> 1 = 1
-    assert_eq!(mb3.drain_count(), 1);
-}
-
-#[test]
-fn drain_count_does_not_mutate() {
-    let mut mb: Mailbox<u64> = Mailbox::new(10);
-    for i in 0..5 {
-        mb.push(i);
-    }
-    let dc1 = mb.drain_count();
-    let dc2 = mb.drain_count();
-    assert_eq!(dc1, dc2);
-    assert_eq!(mb.len(), 5);
-}
-
-#[test]
-fn drain_count_large_waterlevel() {
-    let mut mb: Mailbox<u64> = Mailbox::new(usize::MAX);
-    for i in 0..100 {
-        mb.push(i);
-    }
-    // len=100 < waterlevel=usize::MAX → always full drain
-    assert_eq!(mb.drain_count(), 100);
-}
-
-#[test]
-fn mailbox_with_struct_messages() {
-    let mut mb: Mailbox<TestMsg> = Mailbox::new(10);
-    mb.push(TestMsg(1));
-    mb.push(TestMsg(2));
-    assert_eq!(mb.pop(), Some(TestMsg(1)));
-    assert_eq!(mb.pop(), Some(TestMsg(2)));
-    assert!(mb.is_empty());
-}
-
-// ── ActorPool tests ─────────────────────────────────────────────────
-
-#[test]
-fn pool_new_is_empty() {
-    let pool = ActorPool::new();
-    assert_eq!(pool.len(), 0);
-}
-
-#[test]
-fn pool_insert_increments_len() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    pool.insert(addr, actor);
-    assert_eq!(pool.len(), 1);
-
-    let addr2 = make_addr(2);
-    let (actor2, _) = make_test_actor(addr2);
-    pool.insert(addr2, actor2);
-    assert_eq!(pool.len(), 2);
-}
-
-#[test]
-fn pool_remove_returns_actor() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    pool.insert(addr, actor);
-    assert!(pool.remove(&addr).is_some());
-    assert_eq!(pool.len(), 0);
-}
-
-#[test]
-fn pool_remove_unknown_returns_none() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(99);
-    assert!(pool.remove(&addr).is_none());
-}
-
-#[test]
-fn pool_deliver_correct_type() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    pool.insert(addr, actor);
-
-    let msg: Box<dyn Any + Send> = Box::new(42u64);
-    assert!(pool.deliver(&addr, msg));
-}
-
-#[test]
-fn pool_deliver_unknown_addr() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(99);
-    let msg: Box<dyn Any + Send> = Box::new(42u64);
-    assert!(!pool.deliver(&addr, msg));
-}
-
-#[test]
-fn pool_deliver_wrong_type() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    pool.insert(addr, actor);
-
-    // Actor expects u64, we send String — queued (type check deferred to tick)
-    let msg: Box<dyn Any + Send> = Box::new("wrong type".to_string());
-    assert!(pool.deliver(&addr, msg));
-}
-
-#[test]
-fn pool_tick_all_processes_messages() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, counter) = make_test_actor(addr);
-    pool.insert(addr, actor);
-
-    // Deliver 3 messages
-    pool.deliver(&addr, Box::new(1u64));
-    pool.deliver(&addr, Box::new(2u64));
-    pool.deliver(&addr, Box::new(3u64));
-
-    let stub = StubContextInner { waterlevel: 100 };
-    let processed = pool.tick_all(&stub);
-    assert_eq!(processed, 3);
-    assert_eq!(counter.load(Ordering::Relaxed), 3);
-}
-
-#[test]
-fn pool_tick_all_empty_returns_zero() {
-    let mut pool = ActorPool::new();
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    pool.insert(addr, actor);
-
-    // No messages delivered
-    let stub = StubContextInner { waterlevel: 100 };
-    let processed = pool.tick_all(&stub);
-    assert_eq!(processed, 0);
-}
-
-// ── Worker tests ────────────────────────────────────────────────────
-
-#[test]
-fn worker_tick_once_no_work() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
-    let transfer_tx = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
-
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx],
-        spawn_txs: &[spawn_tx],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
-
-    assert!(!worker.tick_once(&tc));
-}
-
-#[test]
-fn worker_tick_once_drains_spawns() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
-    let transfer_tx = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-
-    let addr = make_addr(1);
-    let (actor, _) = make_test_actor(addr);
-    spawn_tx.try_send((addr, actor)).ok().unwrap();
-
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
-
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx],
-        spawn_txs: &[spawn_tx],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
-
-    assert!(worker.tick_once(&tc));
-    assert_eq!(worker.pool.len(), 1);
-}
-
-#[test]
-fn worker_tick_once_drains_transfers() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
-    let transfer_tx = transfer_rx.new_sender();
-    let transfer_tx2 = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-    let spawn_tx2 = spawn_rx.new_sender();
-
-    let addr = make_addr(1);
-    let (actor, counter) = make_test_actor(addr);
-
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-
-    // Spawn the actor first
-    spawn_tx.try_send((addr, actor)).ok().unwrap();
-
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
-
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx2],
-        spawn_txs: &[spawn_tx2],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
-
-    worker.tick_once(&tc); // drain spawns
-
-    // Now send a transfer envelope
-    let envelope = Envelope::new(addr, Box::new(42u64));
-    transfer_tx.try_send(envelope).ok().unwrap();
-
-    // Tick again to drain transfers + tick actors
-    let did_work = worker.tick_once(&tc);
-    assert!(did_work);
-    assert_eq!(counter.load(Ordering::Relaxed), 1);
-}
-
-#[test]
-fn worker_tick_once_processes_messages() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
-    let transfer_tx = transfer_rx.new_sender();
-    let transfer_tx2 = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-    let spawn_tx2 = spawn_rx.new_sender();
-
-    let addr = make_addr(1);
-    let (actor, counter) = make_test_actor(addr);
-
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-
-    spawn_tx.try_send((addr, actor)).ok().unwrap();
-
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
-
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx2],
-        spawn_txs: &[spawn_tx2],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
-
-    worker.tick_once(&tc); // spawn
-
-    // Deliver multiple messages
-    for i in 0..5u64 {
-        transfer_tx
-            .try_send(Envelope::new(addr, Box::new(i)))
+    /// Enqueue a u64 message (drained on next tick, phase 2).
+    fn send(&self, id: u8, val: u64) {
+        self.feed_transfer
+            .try_send(Envelope::new(addr(id), Box::new(val)))
             .ok()
             .unwrap();
     }
 
-    worker.tick_once(&tc); // transfer + tick
-    assert_eq!(counter.load(Ordering::Relaxed), 5);
-}
-
-#[test]
-fn worker_tick_once_multiple_spawns() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
-    let transfer_tx = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-
-    for i in 0..5u8 {
-        let addr = make_addr(i);
-        let (actor, _) = make_test_actor(addr);
-        spawn_tx.try_send((addr, actor)).ok().unwrap();
+    /// Enqueue a wrong-typed message (String instead of u64).
+    fn send_bad(&self, id: u8) {
+        self.feed_transfer
+            .try_send(Envelope::new(addr(id), Box::new("bad".to_string())))
+            .ok()
+            .unwrap();
     }
 
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
+    /// Remove an actor from the pool (immediate, no tick needed).
+    fn remove(&mut self, id: u8) {
+        self.worker.pool.remove(&addr(id));
+    }
 
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
+    /// Run one tick of the worker loop.
+    fn tick(&mut self) {
+        let tc = TickContext {
+            address_map: &self.address_map,
+            transfer_txs: &self.tc_transfer_txs,
+            spawn_txs: &self.tc_spawn_txs,
+            placement: &self.placement,
+            inbox_registry: &self.inbox_registry,
+            config: &self.config,
+        };
+        self.worker.tick_once(&tc);
+    }
 
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx],
-        spawn_txs: &[spawn_tx],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
+    // ── Readouts ───────────────────────────────────────────────────
 
-    assert!(worker.tick_once(&tc));
-    assert_eq!(worker.pool.len(), 5);
+    fn handled(&self, id: u8) -> usize {
+        self.counters[&id].load(Ordering::Relaxed)
+    }
+
+    fn pool_len(&self) -> usize {
+        self.worker.pool.len()
+    }
+
+    fn depth(&self) -> usize {
+        self.stats.total_mailbox_depth.load(Ordering::Relaxed)
+    }
+
+    fn processed(&self) -> u64 {
+        self.stats.messages_processed.load(Ordering::Relaxed)
+    }
+
+    fn num_actors_stat(&self) -> usize {
+        self.stats.num_actors.load(Ordering::Relaxed)
+    }
+}
+
+// ── Step-driven runner ─────────────────────────────────────────────
+
+enum Step {
+    Spawn(u8),
+    Send(u8, u64),
+    SendBad(u8),
+    Remove(u8),
+    Tick,
+    Expect { pool_len: usize, depth: usize, processed: u64 },
+    ExpectHandled(u8, usize),
+}
+
+fn run(steps: &[Step]) {
+    run_with(RuntimeConfig::default(), steps);
+}
+
+fn run_with(config: RuntimeConfig, steps: &[Step]) {
+    let mut env = Env::with_config(config);
+    for (i, step) in steps.iter().enumerate() {
+        match step {
+            Step::Spawn(id) => env.spawn(*id),
+            Step::Send(id, val) => env.send(*id, *val),
+            Step::SendBad(id) => env.send_bad(*id),
+            Step::Remove(id) => env.remove(*id),
+            Step::Tick => env.tick(),
+            Step::Expect { pool_len, depth, processed } => {
+                assert_eq!(env.pool_len(), *pool_len, "step {i}: pool_len");
+                assert_eq!(env.depth(), *depth, "step {i}: depth");
+                assert_eq!(env.processed(), *processed, "step {i}: processed");
+            }
+            Step::ExpectHandled(id, n) => {
+                assert_eq!(env.handled(*id), *n, "step {i}: handled({})", id);
+            }
+        }
+    }
+}
+
+// ── Tests ──────────────────────────────────────────────────────────
+
+#[test]
+fn spawn_send_process() {
+    run(&[
+        Step::Spawn(1),
+        Step::Spawn(2),
+        Step::Tick,
+        Step::Expect { pool_len: 2, depth: 0, processed: 0 },
+
+        Step::Send(1, 10),
+        Step::Send(1, 20),
+        Step::Send(2, 30),
+        Step::Tick,
+        Step::Expect { pool_len: 2, depth: 0, processed: 3 },
+        Step::ExpectHandled(1, 2),
+        Step::ExpectHandled(2, 1),
+    ]);
 }
 
 #[test]
-fn worker_tick_once_wrong_type_no_panic() {
-    let transfer_rx = Receiver::<Envelope>::new(64);
-    let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
+fn remove_drops_future_messages() {
+    run(&[
+        Step::Spawn(1),
+        Step::Spawn(2),
+        Step::Tick,
 
-    let transfer_tx = transfer_rx.new_sender();
-    let transfer_tx2 = transfer_rx.new_sender();
-    let spawn_tx = spawn_rx.new_sender();
-    let spawn_tx2 = spawn_rx.new_sender();
+        // Remove actor 1 directly from pool
+        Step::Remove(1),
+        Step::Expect { pool_len: 1, depth: 0, processed: 0 },
 
-    let addr = make_addr(1);
-    let (actor, counter) = make_test_actor(addr);
+        // Messages to actor 1 are drained from the transfer queue
+        // but pool.deliver finds no slot — silently dropped
+        Step::Send(1, 42),
+        Step::Send(2, 99),
+        Step::Tick,
 
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-
-    spawn_tx.try_send((addr, actor)).ok().unwrap();
-
-    let address_map = AddressMap::new();
-    let placement = Placement::new(1);
-    let inbox_registry = InboxRegistry::new();
-    let config = RuntimeConfig::default();
-
-    let tc = TickContext {
-        address_map: &address_map,
-        transfer_txs: &[transfer_tx2],
-        spawn_txs: &[spawn_tx2],
-        placement: &placement,
-        inbox_registry: &inbox_registry,
-        config: &config,
-    };
-
-    worker.tick_once(&tc); // spawn
-
-    // Send wrong type (String instead of u64) — should not panic
-    let bad_envelope = Envelope::new(addr, Box::new("wrong".to_string()));
-    transfer_tx.try_send(bad_envelope).ok().unwrap();
-
-    // Send correct type after
-    let good_envelope = Envelope::new(addr, Box::new(99u64));
-    transfer_tx.try_send(good_envelope).ok().unwrap();
-
-    worker.tick_once(&tc); // transfer + tick
-    // The correct message should still be processed
-    assert_eq!(counter.load(Ordering::Relaxed), 1);
+        Step::Expect { pool_len: 1, depth: 0, processed: 1 },
+        Step::ExpectHandled(1, 0),
+        Step::ExpectHandled(2, 1),
+    ]);
 }
 
 #[test]
-fn worker_run_stops_on_signal() {
+fn wrong_type_silently_dropped() {
+    run(&[
+        Step::Spawn(1),
+        Step::Tick,
+
+        // Mix correct (u64) and incorrect (String) types
+        Step::Send(1, 1),
+        Step::SendBad(1),
+        Step::Send(1, 2),
+        Step::SendBad(1),
+        Step::SendBad(1),
+        Step::Send(1, 3),
+        Step::Tick,
+
+        // All 6 popped from mailbox ("processed" by the pool),
+        // but only the 3 u64 messages were handled by the actor
+        Step::Expect { pool_len: 1, depth: 0, processed: 6 },
+        Step::ExpectHandled(1, 3),
+    ]);
+}
+
+#[test]
+fn backpressure_drains_half() {
+    let config = RuntimeConfig {
+        mailbox_waterlevel: 4,
+        ..Default::default()
+    };
+
+    run_with(config, &[
+        Step::Spawn(1),
+        Step::Tick,
+
+        // Send 10 messages
+        Step::Send(1, 0), Step::Send(1, 1), Step::Send(1, 2), Step::Send(1, 3),
+        Step::Send(1, 4), Step::Send(1, 5), Step::Send(1, 6), Step::Send(1, 7),
+        Step::Send(1, 8), Step::Send(1, 9),
+
+        // Tick 1: 10 in mailbox, drain_count(10, 4) = 5
+        Step::Tick,
+        Step::Expect { pool_len: 1, depth: 5, processed: 5 },
+
+        // Tick 2: 5 remaining, drain_count(5, 4) = 2
+        Step::Tick,
+        Step::Expect { pool_len: 1, depth: 3, processed: 7 },
+
+        // Tick 3: 3 remaining, drain_count(3, 4) = 3 (below waterlevel → all)
+        Step::Tick,
+        Step::Expect { pool_len: 1, depth: 0, processed: 10 },
+        Step::ExpectHandled(1, 10),
+    ]);
+}
+
+#[test]
+fn spawn_and_send_same_tick() {
+    // Spawn is phase 1, transfer is phase 2, processing is phase 3.
+    // All three happen within a single tick_once call.
+    run(&[
+        Step::Spawn(1),
+        Step::Send(1, 42),
+        Step::Tick,
+        Step::Expect { pool_len: 1, depth: 0, processed: 1 },
+        Step::ExpectHandled(1, 1),
+    ]);
+}
+
+#[test]
+fn stats_track_pool_mutations() {
+    let mut env = Env::new();
+
+    // Before any tick, stats are zeroed
+    assert_eq!(env.num_actors_stat(), 0);
+    assert_eq!(env.depth(), 0);
+    assert_eq!(env.processed(), 0);
+
+    // Spawn 3 + tick → stats reflect 3 actors
+    env.spawn(1);
+    env.spawn(2);
+    env.spawn(3);
+    env.tick();
+    assert_eq!(env.num_actors_stat(), 3);
+
+    // Send 5 to actor 1 + tick → processed increases
+    for i in 0..5 {
+        env.send(1, i);
+    }
+    env.tick();
+    assert_eq!(env.processed(), 5);
+    assert_eq!(env.depth(), 0);
+    assert_eq!(env.num_actors_stat(), 3);
+
+    // Remove actor 2 + tick → stats update
+    env.remove(2);
+    env.tick();
+    assert_eq!(env.num_actors_stat(), 2);
+    assert_eq!(env.pool_len(), 2);
+}
+
+/// A long mixed-action sequence: spawns, sends, removes, wrong types,
+/// and backpressure — all in one run.
+#[test]
+fn interleaved_lifecycle() {
+    run(&[
+        // ── Phase 1: build the pool ────────────────────────────────
+        Step::Spawn(1),
+        Step::Spawn(2),
+        Step::Spawn(3),
+        Step::Tick,
+        Step::Expect { pool_len: 3, depth: 0, processed: 0 },
+
+        // ── Phase 2: normal message flow ───────────────────────────
+        Step::Send(1, 100),
+        Step::Send(2, 200),
+        Step::Send(3, 300),
+        Step::Tick,
+        Step::ExpectHandled(1, 1),
+        Step::ExpectHandled(2, 1),
+        Step::ExpectHandled(3, 1),
+        Step::Expect { pool_len: 3, depth: 0, processed: 3 },
+
+        // ── Phase 3: remove actor 2, send to all 3 ────────────────
+        Step::Remove(2),
+        Step::Send(1, 101),
+        Step::Send(2, 201), // actor 2 gone — dropped at deliver
+        Step::Send(3, 301),
+        Step::Tick,
+        Step::Expect { pool_len: 2, depth: 0, processed: 5 },
+        Step::ExpectHandled(1, 2),
+        Step::ExpectHandled(2, 1), // unchanged since removal
+        Step::ExpectHandled(3, 2),
+
+        // ── Phase 4: late spawn + immediate send ───────────────────
+        Step::Spawn(4),
+        Step::Send(4, 400),
+        Step::Tick,
+        Step::Expect { pool_len: 3, depth: 0, processed: 6 },
+        Step::ExpectHandled(4, 1),
+
+        // ── Phase 5: bad types mixed with good ─────────────────────
+        Step::SendBad(1),
+        Step::SendBad(1),
+        Step::SendBad(1),
+        Step::Send(1, 999),
+        Step::Tick,
+        // 4 popped (3 bad + 1 good), only 1 handled by actor
+        Step::Expect { pool_len: 3, depth: 0, processed: 10 },
+        Step::ExpectHandled(1, 3), // 2 from prior phases + 1 good
+
+        // ── Phase 6: remove all, send to ghosts ────────────────────
+        Step::Remove(1),
+        Step::Remove(3),
+        Step::Remove(4),
+        Step::Expect { pool_len: 0, depth: 0, processed: 10 },
+        Step::Send(1, 0),
+        Step::Send(3, 0),
+        Step::Tick,
+        Step::Expect { pool_len: 0, depth: 0, processed: 10 },
+    ]);
+}
+
+#[test]
+fn run_loop_stops_on_shutdown() {
     let transfer_rx = Receiver::<Envelope>::new(64);
     let spawn_rx = Receiver::<(ActorAddress, Box<dyn AnyActor>)>::new(64);
-
     let transfer_tx = transfer_rx.new_sender();
     let spawn_tx = spawn_rx.new_sender();
 
-    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, Arc::new(WorkerStats::new()));
-    let is_running = AtomicBool::new(false); // start as false → should exit immediately
+    let stats = Arc::new(WorkerStats::new());
+    let mut worker = Worker::new(WorkerId(0), transfer_rx, spawn_rx, stats);
+
+    let is_running = AtomicBool::new(false);
     let backoff = BackoffPolicy::default();
-
     let address_map = AddressMap::new();
     let placement = Placement::new(1);
     let inbox_registry = InboxRegistry::new();
@@ -602,11 +414,7 @@ fn worker_run_stops_on_signal() {
         config: &config,
     };
 
-    // Run in a scoped thread to verify it actually terminates
     thread::scope(|s| {
-        s.spawn(|| {
-            worker.run(&tc, &is_running, &backoff);
-        });
+        s.spawn(|| worker.run(&tc, &is_running, &backoff));
     });
-    // If we get here, the thread exited — test passes
 }