Add comments to new BeaconChainHarness methods.

beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs

@@ -240,6 +240,11 @@ impl BeaconChainHarness {
         debug!("Free attestations processed.");
     }
 
+    /// Signs a message using some validators secret key with the `Fork` info from the latest state
+    /// of the `BeaconChain`.
+    ///
+    /// Useful for producing slashable messages and other objects that `BeaconChainHarness` does
+    /// not produce naturally.
     pub fn validator_sign(
         &self,
         validator_index: usize,
@@ -259,6 +264,11 @@ impl BeaconChainHarness {
         Some(Signature::new(message, domain, &validator.keypair.sk))
     }
 
+    /// Submit a deposit to the `BeaconChain` and, if given a keypair, create a new
+    /// `ValidatorHarness` instance for this validator.
+    ///
+    /// If a new `ValidatorHarness` was created, the validator should become fully operational as
+    /// if the validator were created during `BeaconChainHarness` instantiation.
     pub fn add_deposit(&mut self, deposit: Deposit, keypair: Option<Keypair>) {
         self.beacon_chain.receive_deposit_for_inclusion(deposit);
 
@@ -270,16 +280,19 @@ impl BeaconChainHarness {
         }
     }
 
+    /// Submit a proposer slashing to the `BeaconChain` for inclusion in some block.
     pub fn add_proposer_slashing(&mut self, proposer_slashing: ProposerSlashing) {
         self.beacon_chain
             .receive_proposer_slashing_for_inclusion(proposer_slashing);
     }
 
+    /// Submit an attester slashing to the `BeaconChain` for inclusion in some block.
     pub fn add_attester_slashing(&mut self, attester_slashing: AttesterSlashing) {
         self.beacon_chain
             .receive_attester_slashing_for_inclusion(attester_slashing);
     }
 
+    /// Executes the fork choice rule on the `BeaconChain`, selecting a new canonical head.
     pub fn run_fork_choice(&mut self) {
         self.beacon_chain.fork_choice().unwrap()
     }