diff --git a/finality-aleph/src/sync/mock/backend.rs b/finality-aleph/src/sync/mock/backend.rs
new file mode 100644
index 0000000000..1c77472645
--- /dev/null
+++ b/finality-aleph/src/sync/mock/backend.rs
@@ -0,0 +1,268 @@
+use std::{
+    collections::HashMap,
+    fmt::{Display, Error as FmtError, Formatter},
+    sync::Arc,
+};
+
+use futures::channel::mpsc::{self, UnboundedSender};
+use parking_lot::Mutex;
+
+use crate::sync::{
+    mock::{MockHeader, MockIdentifier, MockJustification, MockNotification},
+    BlockIdentifier, BlockStatus, ChainStatus, ChainStatusNotifier, Finalizer, Header,
+    Justification as JustificationT,
+};
+
+#[derive(Debug)]
+struct MockBlock {
+    header: MockHeader,
+    justification: Option<MockJustification>,
+}
+
+impl MockBlock {
+    fn new(header: MockHeader) -> Self {
+        Self {
+            header,
+            justification: None,
+        }
+    }
+
+    fn header(&self) -> MockHeader {
+        self.header.clone()
+    }
+
+    fn finalize(&mut self, justification: MockJustification) {
+        self.justification = Some(justification);
+    }
+}
+
+struct BackendStorage {
+    blockchain: HashMap<MockIdentifier, MockBlock>,
+    top_finalized: MockIdentifier,
+    best_block: MockIdentifier,
+    genesis_block: MockIdentifier,
+}
+
+#[derive(Clone)]
+pub struct Backend {
+    inner: Arc<Mutex<BackendStorage>>,
+    notification_sender: UnboundedSender<MockNotification>,
+}
+
+pub fn setup() -> (Backend, impl ChainStatusNotifier<MockIdentifier>) {
+    let (notification_sender, notification_receiver) = mpsc::unbounded();
+
+    (Backend::new(notification_sender), notification_receiver)
+}
+
+fn is_predecessor(
+    storage: &HashMap<MockIdentifier, MockBlock>,
+    mut header: MockHeader,
+    maybe_predecessor: MockIdentifier,
+) -> bool {
+    while let Some(parent) = header.parent_id() {
+        if header.id().number() != parent.number() + 1 {
+            break;
+        }
+        if parent == maybe_predecessor {
+            return true;
+        }
+
+        header = match storage.get(&parent) {
+            Some(block) => block.header(),
+            None => return false,
+        }
+    }
+    false
+}
+
+impl Backend {
+    fn new(notification_sender: UnboundedSender<MockNotification>) -> Self {
+        let header = MockHeader::random_parentless(0);
+        let id = header.id();
+
+        let block = MockBlock {
+            header: header.clone(),
+            justification: Some(MockJustification::for_header(header)),
+        };
+
+        let storage = Arc::new(Mutex::new(BackendStorage {
+            blockchain: HashMap::from([(id.clone(), block)]),
+            top_finalized: id.clone(),
+            best_block: id.clone(),
+            genesis_block: id,
+        }));
+
+        Self {
+            inner: storage,
+            notification_sender,
+        }
+    }
+
+    fn notify_imported(&self, id: MockIdentifier) {
+        self.notification_sender
+            .unbounded_send(MockNotification::BlockImported(id))
+            .expect("notification receiver is open");
+    }
+
+    fn notify_finalized(&self, id: MockIdentifier) {
+        self.notification_sender
+            .unbounded_send(MockNotification::BlockFinalized(id))
+            .expect("notification receiver is open");
+    }
+
+    pub fn import(&self, header: MockHeader) {
+        let mut storage = self.inner.lock();
+
+        let parent_id = match header.parent_id() {
+            Some(id) => id,
+            None => panic!("importing block without a parent: {:?}", header),
+        };
+
+        if storage.blockchain.contains_key(&header.id()) {
+            panic!("importing an already imported block: {:?}", header)
+        }
+
+        if !storage.blockchain.contains_key(&parent_id) {
+            panic!("importing block without an imported parent: {:?}", header)
+        }
+
+        if header.id().number() != parent_id.number() + 1 {
+            panic!("importing block without a correct parent: {:?}", header)
+        }
+
+        if header.id().number() > storage.best_block.number()
+            && is_predecessor(
+                &storage.blockchain,
+                header.clone(),
+                storage.best_block.clone(),
+            )
+        {
+            storage.best_block = header.id();
+        }
+
+        storage
+            .blockchain
+            .insert(header.id(), MockBlock::new(header.clone()));
+
+        self.notify_imported(header.id());
+    }
+}
+
+#[derive(Debug)]
+pub struct FinalizerError;
+
+impl Display for FinalizerError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl Finalizer<MockJustification> for Backend {
+    type Error = FinalizerError;
+
+    fn finalize(&self, justification: MockJustification) -> Result<(), Self::Error> {
+        if !justification.is_correct {
+            panic!(
+                "finalizing block with an incorrect justification: {:?}",
+                justification
+            );
+        }
+
+        let mut storage = self.inner.lock();
+
+        let header = justification.header();
+        let parent_id = match justification.header().parent_id() {
+            Some(id) => id,
+            None => panic!("finalizing block without a parent: {:?}", header),
+        };
+
+        let parent_block = match storage.blockchain.get(&parent_id) {
+            Some(block) => block,
+            None => panic!("finalizing block without an imported parent: {:?}", header),
+        };
+
+        if parent_block.justification.is_none() {
+            panic!("finalizing block without a finalized parent: {:?}", header);
+        }
+
+        if parent_id != storage.top_finalized {
+            panic!(
+                "finalizing block whose parent is not top finalized: {:?}. Top is {:?}",
+                header, storage.top_finalized
+            );
+        }
+
+        let id = justification.header().id();
+        let block = match storage.blockchain.get_mut(&id) {
+            Some(block) => block,
+            None => panic!("finalizing a not imported block: {:?}", header),
+        };
+
+        block.finalize(justification);
+        storage.top_finalized = id.clone();
+        // In case finalization changes best block, we set best block, to top finalized.
+        // Whenever a new import happens, best block will update anyway.
+        if !is_predecessor(
+            &storage.blockchain,
+            storage
+                .blockchain
+                .get(&storage.best_block)
+                .unwrap()
+                .header(),
+            id.clone(),
+        ) {
+            storage.best_block = id.clone()
+        }
+        self.notify_finalized(id);
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct StatusError;
+
+impl Display for StatusError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl ChainStatus<MockJustification> for Backend {
+    type Error = StatusError;
+
+    fn status_of(&self, id: MockIdentifier) -> Result<BlockStatus<MockJustification>, Self::Error> {
+        let storage = self.inner.lock();
+        let block = match storage.blockchain.get(&id) {
+            Some(block) => block,
+            None => return Ok(BlockStatus::Unknown),
+        };
+
+        if let Some(justification) = block.justification.clone() {
+            Ok(BlockStatus::Justified(justification))
+        } else {
+            Ok(BlockStatus::Present(block.header()))
+        }
+    }
+
+    fn best_block(&self) -> Result<MockHeader, Self::Error> {
+        let storage = self.inner.lock();
+        let id = storage.best_block.clone();
+        storage
+            .blockchain
+            .get(&id)
+            .map(|b| b.header())
+            .ok_or(StatusError)
+    }
+
+    fn top_finalized(&self) -> Result<MockJustification, Self::Error> {
+        let storage = self.inner.lock();
+        let id = storage.top_finalized.clone();
+        storage
+            .blockchain
+            .get(&id)
+            .and_then(|b| b.justification.clone())
+            .ok_or(StatusError)
+    }
+}
diff --git a/finality-aleph/src/sync/mock.rs b/finality-aleph/src/sync/mock/mod.rs
similarity index 60%
rename from finality-aleph/src/sync/mock.rs
rename to finality-aleph/src/sync/mock/mod.rs
index 2cdc630cf3..8802b26a34 100644
--- a/finality-aleph/src/sync/mock.rs
+++ b/finality-aleph/src/sync/mock/mod.rs
@@ -1,22 +1,38 @@
+use std::hash::Hash;
+
 use codec::{Decode, Encode};
+use sp_core::H256;
+
+use crate::sync::{
+    BlockIdentifier, BlockStatus, ChainStatusNotification, ChainStatusNotifier, Header,
+    Justification as JustificationT, Verifier,
+};
+
+mod backend;
+mod status_notifier;
+mod verifier;
 
-use crate::sync::{BlockIdentifier, Header, Justification};
+type MockNumber = u32;
+type MockHash = H256;
+
+pub use backend::Backend;
+pub use verifier::MockVerifier;
 
 pub type MockPeerId = u32;
 
 #[derive(Clone, Hash, Debug, PartialEq, Eq, Encode, Decode)]
 pub struct MockIdentifier {
-    number: u32,
-    hash: u32,
+    number: MockNumber,
+    hash: MockHash,
 }
 
 impl MockIdentifier {
-    fn new(number: u32, hash: u32) -> Self {
+    fn new(number: MockNumber, hash: MockHash) -> Self {
         MockIdentifier { number, hash }
     }
 
-    pub fn new_random(number: u32) -> Self {
-        MockIdentifier::new(number, rand::random())
+    pub fn new_random(number: MockNumber) -> Self {
+        MockIdentifier::new(number, MockHash::random())
     }
 }
 
@@ -37,7 +53,7 @@ impl MockHeader {
         MockHeader { id, parent }
     }
 
-    pub fn random_parentless(number: u32) -> Self {
+    pub fn random_parentless(number: MockNumber) -> Self {
         let id = MockIdentifier::new_random(number);
         MockHeader { id, parent: None }
     }
@@ -84,15 +100,26 @@ impl Header for MockHeader {
 #[derive(Clone, Hash, Debug, PartialEq, Eq, Encode, Decode)]
 pub struct MockJustification {
     header: MockHeader,
+    is_correct: bool,
 }
 
 impl MockJustification {
     pub fn for_header(header: MockHeader) -> Self {
-        MockJustification { header }
+        Self {
+            header,
+            is_correct: true,
+        }
+    }
+
+    pub fn for_header_incorrect(header: MockHeader) -> Self {
+        Self {
+            header,
+            is_correct: false,
+        }
     }
 }
 
-impl Justification for MockJustification {
+impl JustificationT for MockJustification {
     type Header = MockHeader;
     type Unverified = Self;
 
@@ -104,3 +131,17 @@ impl Justification for MockJustification {
         self
     }
 }
+
+type MockNotification = ChainStatusNotification<MockIdentifier>;
+type MockBlockStatus = BlockStatus<MockJustification>;
+
+pub fn setup() -> (
+    Backend,
+    impl Verifier<MockJustification>,
+    impl ChainStatusNotifier<MockIdentifier>,
+) {
+    let (backend, notifier) = backend::setup();
+    let verifier = MockVerifier;
+
+    (backend, verifier, notifier)
+}
diff --git a/finality-aleph/src/sync/mock/status_notifier.rs b/finality-aleph/src/sync/mock/status_notifier.rs
new file mode 100644
index 0000000000..e915e1849e
--- /dev/null
+++ b/finality-aleph/src/sync/mock/status_notifier.rs
@@ -0,0 +1,30 @@
+use std::fmt::{Display, Error as FmtError, Formatter};
+
+use futures::channel::mpsc::UnboundedReceiver;
+
+use crate::sync::{
+    mock::{MockIdentifier, MockNotification},
+    ChainStatusNotifier,
+};
+
+#[derive(Debug)]
+pub enum Error {
+    StreamClosed,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        write!(f, "{:?}", self)
+    }
+}
+
+#[async_trait::async_trait]
+impl ChainStatusNotifier<MockIdentifier> for UnboundedReceiver<MockNotification> {
+    type Error = Error;
+
+    async fn next(&mut self) -> Result<MockNotification, Self::Error> {
+        <Self as futures::StreamExt>::next(self)
+            .await
+            .ok_or(Error::StreamClosed)
+    }
+}
diff --git a/finality-aleph/src/sync/mock/verifier.rs b/finality-aleph/src/sync/mock/verifier.rs
new file mode 100644
index 0000000000..a8f95318ed
--- /dev/null
+++ b/finality-aleph/src/sync/mock/verifier.rs
@@ -0,0 +1,31 @@
+use std::fmt::{Display, Error as FmtError, Formatter};
+
+use crate::sync::{mock::MockJustification, Verifier};
+
+pub struct MockVerifier;
+
+#[derive(Debug)]
+pub enum Error {
+    IncorrectJustification,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl Verifier<MockJustification> for MockVerifier {
+    type Error = Error;
+
+    fn verify(
+        &mut self,
+        justification: MockJustification,
+    ) -> Result<MockJustification, Self::Error> {
+        if justification.is_correct {
+            Ok(justification)
+        } else {
+            Err(Error::IncorrectJustification)
+        }
+    }
+}