Start working on u64 json issue

eth2/types/Cargo.toml

@@ -31,3 +31,4 @@ tree_hash_derive = "0.2"
 
 [dev-dependencies]
 env_logger = "0.6.0"
+serde_json = "^1.0"

eth2/types/src/beacon_state/committee_cache/tests.rs

@@ -9,7 +9,7 @@ fn default_values() {
     let cache = CommitteeCache::default();
 
     assert_eq!(cache.is_initialized_at(Epoch::new(0)), false);
-    assert_eq!(cache.active_validator_indices(), &[]);
+    assert!(&cache.active_validator_indices().is_empty());
     assert_eq!(cache.get_crosslink_committee_for_shard(0), None);
     assert_eq!(cache.get_attestation_duties(0), None);
     assert_eq!(cache.active_validator_count(), 0);

eth2/types/src/slot_epoch.rs

@@ -191,4 +191,16 @@ mod epoch_tests {
             Epoch::from_ssz_bytes(&max_epoch.as_ssz_bytes()).unwrap()
         );
     }
+
+    #[test]
+    fn epoch_max_value_json() {
+        let x: Epoch = Epoch::from(u64::max_value());
+        let json = serde_json::to_string(&x).expect("should json encode");
+
+        assert_eq!(&json, "18446744073709552000");
+        assert_eq!(
+            serde_json::from_str::<Epoch>(&json).expect("should json decode"),
+            x
+        );
+    }
 }

eth2/types/src/test_utils/builders/testing_proposer_slashing_builder.rs

@@ -39,15 +39,15 @@ impl TestingProposerSlashingBuilder {
             ..header_1.clone()
         };
 
+        let epoch = slot.epoch(T::slots_per_epoch());
+
         header_1.signature = {
             let message = header_1.signed_root();
-            let epoch = slot.epoch(T::slots_per_epoch());
             signer(proposer_index, &message[..], epoch, Domain::BeaconProposer)
         };
 
         header_2.signature = {
             let message = header_2.signed_root();
-            let epoch = slot.epoch(T::slots_per_epoch());
             signer(proposer_index, &message[..], epoch, Domain::BeaconProposer)
         };