Move BeaconStateTestBuilder into test mod

eth2/types/src/beacon_state_tests.rs

@@ -1,3 +1,5 @@
+#[cfg(test)]
+mod tests {
     use crate::{
         beacon_state::BeaconStateError, BeaconState, ChainSpec, Deposit, DepositData, DepositInput,
         Eth1Data, Hash256, Keypair,
@@ -61,10 +63,6 @@ impl BeaconStateTestBuilder {
         }
     }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
-
     #[test]
     pub fn can_produce_genesis_block() {
         let builder = BeaconStateTestBuilder::with_random_validators(2);