diff --git a/src/primitives/mod.rs b/src/primitives/mod.rs
index 5e4bb9c..29a9e42 100644
--- a/src/primitives/mod.rs
+++ b/src/primitives/mod.rs
@@ -3,7 +3,7 @@ use serde::{Deserialize, Serialize};
 
 pub(crate) mod registry;
 
-#[derive(Debug, Clone, Serialize, Deserialize, Deref, DerefMut, From)]
+#[derive(Debug, Clone, Serialize, Deserialize, Deref, DerefMut, From, PartialEq, Eq, Hash)]
 pub(crate) struct BlsPublicKey(bls::PublicKey);
 
 impl BlsPublicKey {
diff --git a/src/sources/mock.rs b/src/sources/mock.rs
new file mode 100644
index 0000000..9d84adc
--- /dev/null
+++ b/src/sources/mock.rs
@@ -0,0 +1,33 @@
+use std::collections::HashMap;
+
+use crate::primitives::{registry::RegistryEntry, BlsPublicKey};
+
+use super::{ExternalSource, SourceError};
+
+pub(crate) struct MockSource {
+    pub(crate) entries: HashMap<BlsPublicKey, RegistryEntry>,
+}
+
+impl MockSource {
+    pub(crate) fn new() -> Self {
+        Self { entries: HashMap::new() }
+    }
+
+    pub(crate) fn add_entry(&mut self, entry: RegistryEntry) {
+        self.entries.insert(entry.validator_pubkey.clone(), entry);
+    }
+}
+
+#[async_trait::async_trait]
+impl ExternalSource for MockSource {
+    fn name(&self) -> &'static str {
+        "mock"
+    }
+
+    async fn get_validators(
+        &self,
+        pubkeys: &[BlsPublicKey],
+    ) -> Result<Vec<RegistryEntry>, SourceError> {
+        Ok(pubkeys.iter().filter_map(|pubkey| self.entries.get(pubkey).cloned()).collect())
+    }
+}
diff --git a/src/sources/mod.rs b/src/sources/mod.rs
index 80a15ee..2f70ec0 100644
--- a/src/sources/mod.rs
+++ b/src/sources/mod.rs
@@ -7,6 +7,10 @@ use crate::primitives::{registry::RegistryEntry, BlsPublicKey};
 /// <https://github.com/lidofinance/lido-keys-api/tree/develop>
 pub(crate) mod kapi;
 
+/// Mock external source for testing.
+#[cfg(test)]
+pub(crate) mod mock;
+
 #[derive(Debug, Error)]
 pub(crate) enum SourceError {
     #[error(transparent)]