diff --git a/code/crates/core-consensus/tests/it/basic.rs b/code/crates/core-consensus/tests/it/basic.rs
new file mode 100644
index 000000000..7726b550b
--- /dev/null
+++ b/code/crates/core-consensus/tests/it/basic.rs
@@ -0,0 +1,121 @@
+#![allow(clippy::needless_update)]
+
+use informalsystems_malachitebft_core_consensus::{
+    process, Effect, Error, Input, Params, Resumable, Resume, State, WalEntry,
+};
+use malachitebft_core_types::{Round, ThresholdParams, ValuePayload};
+use malachitebft_metrics::Metrics;
+use malachitebft_test::utils::validators::make_validators;
+use malachitebft_test::{Height, TestContext, ValidatorSet};
+
+use super::utils::{propose_timeout, wal_entry_to_input};
+
+/// Minimal harness for driving core-consensus deterministically.
+///
+/// This is intentionally small and does **not** attempt to simulate full networking or timing.
+/// It records WAL entries emitted via `Effect::WalAppend` and can replay them after a simulated crash.
+struct Harness {
+    state: State<TestContext>,
+    // In-memory WAL: (height, entry)
+    wal: Vec<(Height, WalEntry<TestContext>)>,
+}
+
+impl Harness {
+    fn new(height: Height, vs: ValidatorSet) -> Self {
+        let ctx = TestContext::new();
+        let params = Params {
+            address: vs
+                .get_by_index(0)
+                .expect("validator set must be non-empty")
+                .address,
+            threshold_params: ThresholdParams::default(),
+            value_payload: ValuePayload::ProposalOnly,
+            enabled: true,
+        };
+
+        Self {
+            state: State::new(ctx, height, vs, params, 128),
+            wal: Vec::new(),
+        }
+    }
+
+    fn run(&mut self, input: Input<TestContext>) {
+        let metrics = Metrics::new();
+
+        // Split borrows so the effect handler doesn't need to borrow `self` while `state` is mutably borrowed.
+        let state = &mut self.state;
+        let wal = &mut self.wal;
+
+        // Metrics expects step_start/step_end pairing; initialize it to the current driver step.
+        metrics.step_start(state.driver.step());
+
+        let _res: Result<(), informalsystems_malachitebft_core_consensus::Error<TestContext>> = process!(
+            input: input,
+            state: state,
+            metrics: &metrics,
+            with: effect => {
+                let res: Result<Resume<TestContext>, Error<TestContext>> = match effect {
+                        Effect::WalAppend(height, entry, r) => {
+                            wal.push((height, entry));
+                            Ok(r.resume_with(()))
+                        }
+                        // For this PR we keep the effect handler conservative: always continue.
+                        // Follow-up PRs will add specific effect simulation (signing, publishing, etc.).
+                        other => {
+                            let _ = other;
+                            Ok(Resume::Continue)
+                        }
+                    };
+                res
+            }
+        );
+
+        let _ = _res;
+    }
+
+    fn drain_wal_entries(&self, height: Height) -> Vec<WalEntry<TestContext>> {
+        self.wal
+            .iter()
+            .filter_map(|(h, e)| (*h == height).then(|| e.clone()))
+            .collect()
+    }
+}
+
+#[test]
+fn wal_entries_can_be_captured_and_replayed_in_memory() {
+    let [(v1, _sk1), (v2, _sk2), (v3, _sk3), (v4, _sk4)] = make_validators([1, 1, 1, 1]);
+    let vs = ValidatorSet::new(vec![v1, v2, v3, v4]);
+
+    // First run: start height and trigger a persisted timeout.
+    let mut h1 = Harness::new(Height::new(1), vs.clone());
+
+    h1.run(Input::StartHeight(Height::new(1), vs.clone(), false, None));
+
+    h1.run(Input::TimeoutElapsed(propose_timeout(0)));
+
+    let wal_entries = h1.drain_wal_entries(Height::new(1));
+    assert!(
+        wal_entries
+            .iter()
+            .any(|e| matches!(e, WalEntry::Timeout(t) if t.round == Round::new(0))),
+        "expected a timeout WAL entry for round 0"
+    );
+
+    // Simulated crash/restart: new harness, replay WAL entries as inputs.
+    let vs2 = vs;
+    let mut h2 = Harness::new(Height::new(1), vs2.clone());
+    h2.run(Input::StartHeight(Height::new(1), vs2, true, None));
+
+    for entry in wal_entries {
+        h2.run(wal_entry_to_input(entry));
+    }
+
+    // After replay, we should have persisted the same timeout again deterministically.
+    let wal_entries_2 = h2.drain_wal_entries(Height::new(1));
+    assert!(
+        wal_entries_2
+            .iter()
+            .any(|e| matches!(e, WalEntry::Timeout(t) if t.round == Round::new(0))),
+        "expected timeout WAL entry after replay"
+    );
+}
diff --git a/code/crates/core-consensus/tests/it/main.rs b/code/crates/core-consensus/tests/it/main.rs
new file mode 100644
index 000000000..8d00bd26d
--- /dev/null
+++ b/code/crates/core-consensus/tests/it/main.rs
@@ -0,0 +1,3 @@
+pub mod basic;
+
+mod utils;
diff --git a/code/crates/core-consensus/tests/it/utils.rs b/code/crates/core-consensus/tests/it/utils.rs
new file mode 100644
index 000000000..370426e6c
--- /dev/null
+++ b/code/crates/core-consensus/tests/it/utils.rs
@@ -0,0 +1,26 @@
+use informalsystems_malachitebft_core_consensus::{Input, WalEntry};
+use malachitebft_core_types::{Context, Timeout};
+
+/// Convert a WAL entry back into a core-consensus input for deterministic replay.
+pub fn wal_entry_to_input<Ctx: Context>(entry: WalEntry<Ctx>) -> Input<Ctx> {
+    match entry {
+        WalEntry::ConsensusMsg(msg) => match msg {
+            informalsystems_malachitebft_core_consensus::SignedConsensusMsg::Vote(v) => {
+                Input::Vote(v)
+            }
+            informalsystems_malachitebft_core_consensus::SignedConsensusMsg::Proposal(p) => {
+                Input::Proposal(p)
+            }
+        },
+        WalEntry::Timeout(timeout) => Input::TimeoutElapsed(timeout),
+        WalEntry::ProposedValue(v) => {
+            // For now, treat replay as if the value arrived from consensus gossip.
+            // (Scenarios that require ValueOrigin::Sync will be added in follow-up PRs.)
+            Input::ProposedValue(v, malachitebft_core_types::ValueOrigin::Consensus)
+        }
+    }
+}
+
+pub fn propose_timeout(round: u32) -> Timeout {
+    Timeout::propose(malachitebft_core_types::Round::new(round))
+}