Add additional fake_crypto objects

eth2/utils/bls/src/fake_aggregate_public_key.rs

@@ -0,0 +1,28 @@
+use super::{PublicKey, BLS_PUBLIC_KEY_BYTE_SIZE};
+use bls_aggregates::AggregatePublicKey as RawAggregatePublicKey;
+
+/// A BLS aggregate public key.
+///
+/// This struct is a wrapper upon a base type and provides helper functions (e.g., SSZ
+/// serialization).
+#[derive(Debug, Clone, Default)]
+pub struct FakeAggregatePublicKey {
+    bytes: Vec<u8>,
+}
+
+impl FakeAggregatePublicKey {
+    pub fn new() -> Self {
+        Self::zero()
+    }
+
+    /// Creates a new all-zero's aggregate public key
+    pub fn zero() -> Self {
+        Self {
+            bytes: vec![0; BLS_PUBLIC_KEY_BYTE_SIZE],
+        }
+    }
+
+    pub fn add(&mut self, _public_key: &PublicKey) {
+        // No nothing.
+    }
+}