Dump chain to JSON file

beacon_node/beacon_chain/tests/chain.rs

@@ -15,4 +15,6 @@ fn it_can_produce_blocks() {
     let dump = rig.chain_dump().expect("Chain dump failed.");
 
     assert_eq!(dump.len(), blocks + 1); // + 1 for genesis block.
+
+    rig.dump_to_file("/tmp/chaindump.json".to_string(), &dump);
 }

beacon_node/beacon_chain/tests/utils/test_rig.rs

@@ -6,7 +6,10 @@ use db::{
     stores::{BeaconBlockStore, BeaconStateStore},
     MemoryDB,
 };
+use serde_json::Result as SerdeResult;
 use slot_clock::TestingSlotClock;
+use std::fs::File;
+use std::io::prelude::*;
 use std::sync::Arc;
 use types::{ChainSpec, Keypair, Validator};
 
@@ -87,4 +90,10 @@ impl TestRig {
     pub fn chain_dump(&self) -> Result<Vec<SlotDump>, DumpError> {
         self.beacon_chain.chain_dump()
     }
+
+    pub fn dump_to_file(&self, filename: String, chain_dump: &Vec<SlotDump>) {
+        let json = serde_json::to_string(chain_dump).unwrap();
+        let mut file = File::create(filename).unwrap();
+        file.write_all(json.as_bytes());
+    }
 }