Allow test_harness to load validators from file

Also adds a command to test_harness binary to generate validators

beacon_node/beacon_chain/test_harness/src/prepare.rs

@@ -0,0 +1,35 @@
+use crate::beacon_chain_harness::generate_deposits_with_deterministic_keypairs;
+use clap::{value_t, ArgMatches};
+use log::debug;
+use serde_yaml;
+use std::path::Path;
+use std::{fs, fs::File};
+use types::*;
+
+const KEYPAIRS_FILE: &str = "keypairs.yaml";
+const DEPOSITS_FILE: &str = "deposits.yaml";
+
+pub fn prepare(matches: &ArgMatches, spec: &ChainSpec) {
+    let validator_count = value_t!(matches.value_of("validator_count"), usize)
+        .expect("Validator count is required argument");
+    let genesis_time =
+        value_t!(matches.value_of("genesis_time"), u64).expect("Genesis time is required argument");
+    let output_dir = matches
+        .value_of("output_dir")
+        .expect("Output dir has a default value.");
+
+    let (keypairs, deposits) =
+        generate_deposits_with_deterministic_keypairs(validator_count, genesis_time, &spec);
+
+    debug!("Created keypairs and deposits, writing to file...");
+
+    fs::create_dir_all(Path::new(output_dir)).unwrap();
+
+    let keypairs_path = Path::new(output_dir).join(KEYPAIRS_FILE);
+    let keypairs_file = File::create(keypairs_path).unwrap();
+    serde_yaml::to_writer(keypairs_file, &keypairs).unwrap();
+
+    let deposits_path = Path::new(output_dir).join(DEPOSITS_FILE);
+    let deposits_file = File::create(deposits_path).unwrap();
+    serde_yaml::to_writer(deposits_file, &deposits).unwrap();
+}