diff --git a/beacon_node/beacon_chain/src/snapshot_cache.rs b/beacon_node/beacon_chain/src/snapshot_cache.rs
index b386c22c29..e273c35218 100644
--- a/beacon_node/beacon_chain/src/snapshot_cache.rs
+++ b/beacon_node/beacon_chain/src/snapshot_cache.rs
@@ -280,19 +280,17 @@ impl<T: EthSpec> SnapshotCache<T> {
 mod test {
     use super::*;
     use crate::test_utils::{BeaconChainHarness, EphemeralHarnessType};
-    use store::StoreConfig;
     use types::{
         test_utils::generate_deterministic_keypair, BeaconBlock, Epoch, MainnetEthSpec,
         SignedBeaconBlock, Slot,
     };
 
     fn get_harness() -> BeaconChainHarness<EphemeralHarnessType<MainnetEthSpec>> {
-        let harness = BeaconChainHarness::new_with_store_config(
-            MainnetEthSpec,
-            None,
-            types::test_utils::generate_deterministic_keypairs(1),
-            StoreConfig::default(),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .default_spec()
+            .deterministic_keypairs(1)
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
diff --git a/beacon_node/beacon_chain/src/test_utils.rs b/beacon_node/beacon_chain/src/test_utils.rs
index 11d4af90f4..1be7d746cf 100644
--- a/beacon_node/beacon_chain/src/test_utils.rs
+++ b/beacon_node/beacon_chain/src/test_utils.rs
@@ -21,6 +21,7 @@ use rand::rngs::StdRng;
 use rand::Rng;
 use rand::SeedableRng;
 use rayon::prelude::*;
+use slog::Logger;
 use slot_clock::TestingSlotClock;
 use state_processing::state_advance::complete_state_advance;
 use std::borrow::Cow;
@@ -61,6 +62,12 @@ pub type BaseHarnessType<TEthSpec, THotStore, TColdStore> =
 pub type DiskHarnessType<E> = BaseHarnessType<E, LevelDB<E>, LevelDB<E>>;
 pub type EphemeralHarnessType<E> = BaseHarnessType<E, MemoryStore<E>, MemoryStore<E>>;
 
+type BoxedMutator<E, Hot, Cold> = Box<
+    dyn FnOnce(
+        BeaconChainBuilder<BaseHarnessType<E, Hot, Cold>>,
+    ) -> BeaconChainBuilder<BaseHarnessType<E, Hot, Cold>>,
+>;
+
 pub type AddBlocksResult<E> = (
     HashMap<Slot, SignedBeaconBlockHash>,
     HashMap<Slot, BeaconStateHash>,
@@ -134,6 +141,216 @@ pub fn test_spec<E: EthSpec>() -> ChainSpec {
     spec
 }
 
+pub struct Builder<T: BeaconChainTypes> {
+    eth_spec_instance: T::EthSpec,
+    spec: Option<ChainSpec>,
+    validator_keypairs: Option<Vec<Keypair>>,
+    chain_config: Option<ChainConfig>,
+    store_config: Option<StoreConfig>,
+    #[allow(clippy::type_complexity)]
+    store: Option<Arc<HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>>>,
+    initial_mutator: Option<BoxedMutator<T::EthSpec, T::HotStore, T::ColdStore>>,
+    store_mutator: Option<BoxedMutator<T::EthSpec, T::HotStore, T::ColdStore>>,
+    log: Logger,
+}
+
+impl<E: EthSpec> Builder<EphemeralHarnessType<E>> {
+    pub fn fresh_ephemeral_store(mut self) -> Self {
+        let spec = self.spec.as_ref().expect("cannot build without spec");
+        let validator_keypairs = self
+            .validator_keypairs
+            .clone()
+            .expect("cannot build without validator keypairs");
+
+        let store = Arc::new(
+            HotColdDB::open_ephemeral(
+                self.store_config.clone().unwrap_or_default(),
+                spec.clone(),
+                self.log.clone(),
+            )
+            .unwrap(),
+        );
+        let mutator = move |builder: BeaconChainBuilder<_>| {
+            let genesis_state = interop_genesis_state::<E>(
+                &validator_keypairs,
+                HARNESS_GENESIS_TIME,
+                builder.get_spec(),
+            )
+            .expect("should generate interop state");
+            builder
+                .genesis_state(genesis_state)
+                .expect("should build state using recent genesis")
+        };
+        self.store = Some(store);
+        self.store_mutator(Box::new(mutator))
+    }
+}
+
+impl<E: EthSpec> Builder<DiskHarnessType<E>> {
+    /// Disk store, start from genesis.
+    pub fn fresh_disk_store(mut self, store: Arc<HotColdDB<E, LevelDB<E>, LevelDB<E>>>) -> Self {
+        let validator_keypairs = self
+            .validator_keypairs
+            .clone()
+            .expect("cannot build without validator keypairs");
+
+        let mutator = move |builder: BeaconChainBuilder<_>| {
+            let genesis_state = interop_genesis_state::<E>(
+                &validator_keypairs,
+                HARNESS_GENESIS_TIME,
+                builder.get_spec(),
+            )
+            .expect("should generate interop state");
+            builder
+                .genesis_state(genesis_state)
+                .expect("should build state using recent genesis")
+        };
+        self.store = Some(store);
+        self.store_mutator(Box::new(mutator))
+    }
+
+    /// Disk store, resume.
+    pub fn resumed_disk_store(mut self, store: Arc<HotColdDB<E, LevelDB<E>, LevelDB<E>>>) -> Self {
+        let mutator = move |builder: BeaconChainBuilder<_>| {
+            builder
+                .resume_from_db()
+                .expect("should resume from database")
+        };
+        self.store = Some(store);
+        self.store_mutator(Box::new(mutator))
+    }
+}
+
+impl<E, Hot, Cold> Builder<BaseHarnessType<E, Hot, Cold>>
+where
+    E: EthSpec,
+    Hot: ItemStore<E>,
+    Cold: ItemStore<E>,
+{
+    pub fn new(eth_spec_instance: E) -> Self {
+        Self {
+            eth_spec_instance,
+            spec: None,
+            validator_keypairs: None,
+            chain_config: None,
+            store_config: None,
+            store: None,
+            initial_mutator: None,
+            store_mutator: None,
+            log: test_logger(),
+        }
+    }
+
+    pub fn deterministic_keypairs(self, num_keypairs: usize) -> Self {
+        self.keypairs(types::test_utils::generate_deterministic_keypairs(
+            num_keypairs,
+        ))
+    }
+
+    pub fn keypairs(mut self, validator_keypairs: Vec<Keypair>) -> Self {
+        self.validator_keypairs = Some(validator_keypairs);
+        self
+    }
+
+    pub fn default_spec(self) -> Self {
+        self.spec_or_default(None)
+    }
+
+    pub fn spec(self, spec: ChainSpec) -> Self {
+        self.spec_or_default(Some(spec))
+    }
+
+    pub fn spec_or_default(mut self, spec: Option<ChainSpec>) -> Self {
+        self.spec = Some(spec.unwrap_or_else(test_spec::<E>));
+        self
+    }
+
+    /// This mutator will be run before the `store_mutator`.
+    pub fn initial_mutator(mut self, mutator: BoxedMutator<E, Hot, Cold>) -> Self {
+        assert!(
+            self.initial_mutator.is_none(),
+            "initial mutator already set"
+        );
+        self.initial_mutator = Some(mutator);
+        self
+    }
+
+    /// This mutator will be run after the `initial_mutator`.
+    pub fn store_mutator(mut self, mutator: BoxedMutator<E, Hot, Cold>) -> Self {
+        assert!(self.store_mutator.is_none(), "store mutator already set");
+        self.store_mutator = Some(mutator);
+        self
+    }
+
+    /// Purposefully replace the `store_mutator`.
+    pub fn override_store_mutator(mut self, mutator: BoxedMutator<E, Hot, Cold>) -> Self {
+        assert!(self.store_mutator.is_some(), "store mutator not set");
+        self.store_mutator = Some(mutator);
+        self
+    }
+
+    pub fn chain_config(mut self, chain_config: ChainConfig) -> Self {
+        self.chain_config = Some(chain_config);
+        self
+    }
+
+    pub fn build(self) -> BeaconChainHarness<BaseHarnessType<E, Hot, Cold>> {
+        let (shutdown_tx, shutdown_receiver) = futures::channel::mpsc::channel(1);
+
+        let log = test_logger();
+        let spec = self.spec.expect("cannot build without spec");
+        let validator_keypairs = self
+            .validator_keypairs
+            .expect("cannot build without validator keypairs");
+
+        let mut builder = BeaconChainBuilder::new(self.eth_spec_instance)
+            .logger(log.clone())
+            .custom_spec(spec)
+            .store(self.store.expect("cannot build without store"))
+            .store_migrator_config(MigratorConfig::default().blocking())
+            .dummy_eth1_backend()
+            .expect("should build dummy backend")
+            .shutdown_sender(shutdown_tx)
+            .chain_config(self.chain_config.unwrap_or_default())
+            .event_handler(Some(ServerSentEventHandler::new_with_capacity(
+                log.clone(),
+                5,
+            )))
+            .monitor_validators(true, vec![], log);
+
+        builder = if let Some(mutator) = self.initial_mutator {
+            mutator(builder)
+        } else {
+            builder
+        };
+
+        builder = if let Some(mutator) = self.store_mutator {
+            mutator(builder)
+        } else {
+            builder
+        };
+
+        // Initialize the slot clock only if it hasn't already been initialized.
+        builder = if builder.get_slot_clock().is_none() {
+            builder
+                .testing_slot_clock(HARNESS_SLOT_TIME)
+                .expect("should configure testing slot clock")
+        } else {
+            builder
+        };
+
+        let chain = builder.build().expect("should build");
+
+        BeaconChainHarness {
+            spec: chain.spec.clone(),
+            chain: Arc::new(chain),
+            validator_keypairs,
+            shutdown_receiver,
+            rng: make_rng(),
+        }
+    }
+}
+
 /// A testing harness which can instantiate a `BeaconChain` and populate it with blocks and
 /// attestations.
 ///
@@ -158,205 +375,14 @@ pub type HarnessSyncContributions<E> = Vec<(
     Option<SignedContributionAndProof<E>>,
 )>;
 
-impl<E: EthSpec> BeaconChainHarness<EphemeralHarnessType<E>> {
-    pub fn new(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        validator_keypairs: Vec<Keypair>,
-    ) -> Self {
-        Self::new_with_store_config(
-            eth_spec_instance,
-            spec,
-            validator_keypairs,
-            StoreConfig::default(),
-        )
-    }
-
-    pub fn new_with_store_config(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        validator_keypairs: Vec<Keypair>,
-        config: StoreConfig,
-    ) -> Self {
-        Self::new_with_chain_config(
-            eth_spec_instance,
-            spec,
-            validator_keypairs,
-            config,
-            ChainConfig::default(),
-        )
-    }
-
-    pub fn new_with_chain_config(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        validator_keypairs: Vec<Keypair>,
-        store_config: StoreConfig,
-        chain_config: ChainConfig,
-    ) -> Self {
-        Self::ephemeral_with_mutator(
-            eth_spec_instance,
-            spec,
-            validator_keypairs,
-            store_config,
-            chain_config,
-            |x| x,
-        )
-    }
-
-    pub fn ephemeral_with_mutator(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        validator_keypairs: Vec<Keypair>,
-        store_config: StoreConfig,
-        chain_config: ChainConfig,
-        mutator: impl FnOnce(
-            BeaconChainBuilder<EphemeralHarnessType<E>>,
-        ) -> BeaconChainBuilder<EphemeralHarnessType<E>>,
-    ) -> Self {
-        let spec = spec.unwrap_or_else(test_spec::<E>);
-        let log = test_logger();
-        let store = Arc::new(HotColdDB::open_ephemeral(store_config, spec.clone(), log).unwrap());
-        Self::new_with_mutator(
-            eth_spec_instance,
-            spec,
-            store,
-            validator_keypairs.clone(),
-            chain_config,
-            |mut builder| {
-                builder = mutator(builder);
-                let genesis_state = interop_genesis_state::<E>(
-                    &validator_keypairs,
-                    HARNESS_GENESIS_TIME,
-                    builder.get_spec(),
-                )
-                .expect("should generate interop state");
-                builder
-                    .genesis_state(genesis_state)
-                    .expect("should build state using recent genesis")
-            },
-        )
-    }
-}
-
-impl<E: EthSpec> BeaconChainHarness<DiskHarnessType<E>> {
-    /// Disk store, start from genesis.
-    pub fn new_with_disk_store(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        store: Arc<HotColdDB<E, LevelDB<E>, LevelDB<E>>>,
-        validator_keypairs: Vec<Keypair>,
-    ) -> Self {
-        let spec = spec.unwrap_or_else(test_spec::<E>);
-
-        let chain_config = ChainConfig::default();
-
-        Self::new_with_mutator(
-            eth_spec_instance,
-            spec,
-            store,
-            validator_keypairs.clone(),
-            chain_config,
-            |builder| {
-                let genesis_state = interop_genesis_state::<E>(
-                    &validator_keypairs,
-                    HARNESS_GENESIS_TIME,
-                    builder.get_spec(),
-                )
-                .expect("should generate interop state");
-                builder
-                    .genesis_state(genesis_state)
-                    .expect("should build state using recent genesis")
-            },
-        )
-    }
-
-    /// Disk store, resume.
-    pub fn resume_from_disk_store(
-        eth_spec_instance: E,
-        spec: Option<ChainSpec>,
-        store: Arc<HotColdDB<E, LevelDB<E>, LevelDB<E>>>,
-        validator_keypairs: Vec<Keypair>,
-    ) -> Self {
-        let spec = spec.unwrap_or_else(test_spec::<E>);
-
-        let chain_config = ChainConfig::default();
-
-        Self::new_with_mutator(
-            eth_spec_instance,
-            spec,
-            store,
-            validator_keypairs,
-            chain_config,
-            |builder| {
-                builder
-                    .resume_from_db()
-                    .expect("should resume from database")
-            },
-        )
-    }
-}
-
 impl<E, Hot, Cold> BeaconChainHarness<BaseHarnessType<E, Hot, Cold>>
 where
     E: EthSpec,
     Hot: ItemStore<E>,
     Cold: ItemStore<E>,
 {
-    /// Generic initializer.
-    ///
-    /// This initializer should be able to handle almost any configuration via arguments and the
-    /// provided `mutator` function. Please do not copy and paste this function.
-    pub fn new_with_mutator(
-        eth_spec_instance: E,
-        spec: ChainSpec,
-        store: Arc<HotColdDB<E, Hot, Cold>>,
-        validator_keypairs: Vec<Keypair>,
-        chain_config: ChainConfig,
-        mutator: impl FnOnce(
-            BeaconChainBuilder<BaseHarnessType<E, Hot, Cold>>,
-        ) -> BeaconChainBuilder<BaseHarnessType<E, Hot, Cold>>,
-    ) -> Self {
-        let (shutdown_tx, shutdown_receiver) = futures::channel::mpsc::channel(1);
-
-        let log = test_logger();
-
-        let mut builder = BeaconChainBuilder::new(eth_spec_instance)
-            .logger(log.clone())
-            .custom_spec(spec)
-            .store(store)
-            .store_migrator_config(MigratorConfig::default().blocking())
-            .dummy_eth1_backend()
-            .expect("should build dummy backend")
-            .shutdown_sender(shutdown_tx)
-            .chain_config(chain_config)
-            .event_handler(Some(ServerSentEventHandler::new_with_capacity(
-                log.clone(),
-                5,
-            )))
-            .monitor_validators(true, vec![], log);
-
-        // Caller must initialize genesis state.
-        builder = mutator(builder);
-
-        // Initialize the slot clock only if it hasn't already been initialized.
-        builder = if builder.get_slot_clock().is_none() {
-            builder
-                .testing_slot_clock(HARNESS_SLOT_TIME)
-                .expect("should configure testing slot clock")
-        } else {
-            builder
-        };
-
-        let chain = builder.build().expect("should build");
-
-        Self {
-            spec: chain.spec.clone(),
-            chain: Arc::new(chain),
-            validator_keypairs,
-            shutdown_receiver,
-            rng: make_rng(),
-        }
+    pub fn builder(eth_spec_instance: E) -> Builder<BaseHarnessType<E, Hot, Cold>> {
+        Builder::new(eth_spec_instance)
     }
 
     pub fn logger(&self) -> &slog::Logger {
diff --git a/beacon_node/beacon_chain/src/validator_pubkey_cache.rs b/beacon_node/beacon_chain/src/validator_pubkey_cache.rs
index c1d7ab5d28..2dbe8ce7bf 100644
--- a/beacon_node/beacon_chain/src/validator_pubkey_cache.rs
+++ b/beacon_node/beacon_chain/src/validator_pubkey_cache.rs
@@ -326,7 +326,7 @@ mod test {
     use crate::test_utils::{BeaconChainHarness, EphemeralHarnessType};
     use logging::test_logger;
     use std::sync::Arc;
-    use store::{HotColdDB, StoreConfig};
+    use store::HotColdDB;
     use tempfile::tempdir;
     use types::{
         test_utils::generate_deterministic_keypair, BeaconState, EthSpec, Keypair, MainnetEthSpec,
@@ -336,12 +336,11 @@ mod test {
     type T = EphemeralHarnessType<E>;
 
     fn get_state(validator_count: usize) -> (BeaconState<E>, Vec<Keypair>) {
-        let harness = BeaconChainHarness::new_with_store_config(
-            MainnetEthSpec,
-            None,
-            types::test_utils::generate_deterministic_keypairs(validator_count),
-            StoreConfig::default(),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .default_spec()
+            .deterministic_keypairs(validator_count)
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
diff --git a/beacon_node/beacon_chain/tests/attestation_production.rs b/beacon_node/beacon_chain/tests/attestation_production.rs
index 38877c99de..d2f564146d 100644
--- a/beacon_node/beacon_chain/tests/attestation_production.rs
+++ b/beacon_node/beacon_chain/tests/attestation_production.rs
@@ -5,7 +5,6 @@ extern crate lazy_static;
 
 use beacon_chain::test_utils::{AttestationStrategy, BeaconChainHarness, BlockStrategy};
 use beacon_chain::{StateSkipConfig, WhenSlotSkipped};
-use store::config::StoreConfig;
 use tree_hash::TreeHash;
 use types::{AggregateSignature, EthSpec, Keypair, MainnetEthSpec, RelativeEpoch, Slot};
 
@@ -25,12 +24,11 @@ fn produces_attestations() {
     let num_blocks_produced = MainnetEthSpec::slots_per_epoch() * 4;
     let additional_slots_tested = MainnetEthSpec::slots_per_epoch() * 3;
 
-    let harness = BeaconChainHarness::new_with_store_config(
-        MainnetEthSpec,
-        None,
-        KEYPAIRS[..].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[..].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     let chain = &harness.chain;
 
diff --git a/beacon_node/beacon_chain/tests/attestation_verification.rs b/beacon_node/beacon_chain/tests/attestation_verification.rs
index 26aca88f8c..45d316e3d3 100644
--- a/beacon_node/beacon_chain/tests/attestation_verification.rs
+++ b/beacon_node/beacon_chain/tests/attestation_verification.rs
@@ -14,7 +14,6 @@ use int_to_bytes::int_to_bytes32;
 use state_processing::{
     per_block_processing::errors::AttestationValidationError, per_slot_processing,
 };
-use store::config::StoreConfig;
 use tree_hash::TreeHash;
 use types::{
     test_utils::generate_deterministic_keypair, AggregateSignature, Attestation, BeaconStateError,
@@ -41,12 +40,11 @@ fn get_harness(validator_count: usize) -> BeaconChainHarness<EphemeralHarnessTyp
     // not all.
     spec.target_aggregators_per_committee = 4;
 
-    let harness = BeaconChainHarness::new_with_store_config(
-        MainnetEthSpec,
-        Some(spec),
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .spec(spec)
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     harness.advance_slot();
 
diff --git a/beacon_node/beacon_chain/tests/block_verification.rs b/beacon_node/beacon_chain/tests/block_verification.rs
index d59be85710..93b303c268 100644
--- a/beacon_node/beacon_chain/tests/block_verification.rs
+++ b/beacon_node/beacon_chain/tests/block_verification.rs
@@ -6,7 +6,7 @@ extern crate lazy_static;
 use beacon_chain::test_utils::{
     AttestationStrategy, BeaconChainHarness, BlockStrategy, EphemeralHarnessType,
 };
-use beacon_chain::{BeaconSnapshot, BlockError, ChainConfig, ChainSegmentResult};
+use beacon_chain::{BeaconSnapshot, BlockError, ChainSegmentResult};
 use logging::test_logger;
 use slasher::{Config as SlasherConfig, Slasher};
 use state_processing::{
@@ -15,7 +15,6 @@ use state_processing::{
     per_slot_processing, BlockProcessingError,
 };
 use std::sync::Arc;
-use store::config::StoreConfig;
 use tempfile::tempdir;
 use types::{test_utils::generate_deterministic_keypair, *};
 
@@ -53,12 +52,11 @@ fn get_chain_segment() -> Vec<BeaconSnapshot<E>> {
 }
 
 fn get_harness(validator_count: usize) -> BeaconChainHarness<EphemeralHarnessType<E>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        MainnetEthSpec,
-        None,
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     harness.advance_slot();
 
@@ -841,14 +839,13 @@ fn verify_block_for_gossip_slashing_detection() {
         .unwrap(),
     );
 
-    let harness = BeaconChainHarness::ephemeral_with_mutator(
-        MainnetEthSpec,
-        None,
-        KEYPAIRS.to_vec(),
-        StoreConfig::default(),
-        ChainConfig::default(),
-        |builder| builder.slasher(slasher.clone()),
-    );
+    let inner_slasher = slasher.clone();
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS.to_vec())
+        .fresh_ephemeral_store()
+        .initial_mutator(Box::new(move |builder| builder.slasher(inner_slasher)))
+        .build();
     harness.advance_slot();
 
     let state = harness.get_current_state();
@@ -923,13 +920,11 @@ fn add_base_block_to_altair_chain() {
     // The Altair fork happens at epoch 1.
     spec.altair_fork_epoch = Some(Epoch::new(1));
 
-    let harness = BeaconChainHarness::new_with_chain_config(
-        MainnetEthSpec,
-        Some(spec),
-        KEYPAIRS[..].to_vec(),
-        StoreConfig::default(),
-        ChainConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .spec(spec)
+        .keypairs(KEYPAIRS[..].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     // Move out of the genesis slot.
     harness.advance_slot();
@@ -1042,13 +1037,11 @@ fn add_altair_block_to_base_chain() {
     // Altair never happens.
     spec.altair_fork_epoch = None;
 
-    let harness = BeaconChainHarness::new_with_chain_config(
-        MainnetEthSpec,
-        Some(spec),
-        KEYPAIRS[..].to_vec(),
-        StoreConfig::default(),
-        ChainConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .spec(spec)
+        .keypairs(KEYPAIRS[..].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     // Move out of the genesis slot.
     harness.advance_slot();
diff --git a/beacon_node/beacon_chain/tests/op_verification.rs b/beacon_node/beacon_chain/tests/op_verification.rs
index 34ee8483b4..56e76cffe5 100644
--- a/beacon_node/beacon_chain/tests/op_verification.rs
+++ b/beacon_node/beacon_chain/tests/op_verification.rs
@@ -38,12 +38,11 @@ fn get_store(db_path: &TempDir) -> Arc<HotColdDB> {
 }
 
 fn get_harness(store: Arc<HotColdDB>, validator_count: usize) -> TestHarness {
-    let harness = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        None,
-        store,
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_disk_store(store)
+        .build();
     harness.advance_slot();
     harness
 }
diff --git a/beacon_node/beacon_chain/tests/store_tests.rs b/beacon_node/beacon_chain/tests/store_tests.rs
index afc14dce7b..8a2412b2fa 100644
--- a/beacon_node/beacon_chain/tests/store_tests.rs
+++ b/beacon_node/beacon_chain/tests/store_tests.rs
@@ -61,12 +61,11 @@ fn get_harness(
     store: Arc<HotColdDB<E, LevelDB<E>, LevelDB<E>>>,
     validator_count: usize,
 ) -> TestHarness {
-    let harness = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        None,
-        store,
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_disk_store(store)
+        .build();
     harness.advance_slot();
     harness
 }
@@ -365,12 +364,11 @@ fn delete_blocks_and_states() {
     let store = get_store(&db_path);
     let validators_keypairs =
         types::test_utils::generate_deterministic_keypairs(LOW_VALIDATOR_COUNT);
-    let harness = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        None,
-        store.clone(),
-        validators_keypairs,
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_disk_store(store.clone())
+        .build();
 
     let unforked_blocks: u64 = 4 * E::slots_per_epoch();
 
@@ -492,8 +490,11 @@ fn multi_epoch_fork_valid_blocks_test(
     let store = get_store(&db_path);
     let validators_keypairs =
         types::test_utils::generate_deterministic_keypairs(LOW_VALIDATOR_COUNT);
-    let harness =
-        BeaconChainHarness::new_with_disk_store(MinimalEthSpec, None, store, validators_keypairs);
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_disk_store(store)
+        .build();
 
     let num_fork1_blocks: u64 = num_fork1_blocks_.try_into().unwrap();
     let num_fork2_blocks: u64 = num_fork2_blocks_.try_into().unwrap();
@@ -783,7 +784,11 @@ fn prunes_abandoned_fork_between_two_finalized_checkpoints() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let slots_per_epoch = rig.slots_per_epoch();
     let (mut state, state_root) = rig.get_current_state_and_root();
 
@@ -888,7 +893,11 @@ fn pruning_does_not_touch_abandoned_block_shared_with_canonical_chain() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let slots_per_epoch = rig.slots_per_epoch();
     let (state, state_root) = rig.get_current_state_and_root();
 
@@ -1013,7 +1022,11 @@ fn pruning_does_not_touch_blocks_prior_to_finalization() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let slots_per_epoch = rig.slots_per_epoch();
     let (mut state, state_root) = rig.get_current_state_and_root();
 
@@ -1103,7 +1116,11 @@ fn prunes_fork_growing_past_youngest_finalized_checkpoint() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let (state, state_root) = rig.get_current_state_and_root();
 
     // Fill up 0th epoch with canonical chain blocks
@@ -1241,7 +1258,11 @@ fn prunes_skipped_slots_states() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let (state, state_root) = rig.get_current_state_and_root();
 
     let canonical_slots_zeroth_epoch: Vec<Slot> =
@@ -1360,7 +1381,11 @@ fn finalizes_non_epoch_start_slot() {
     let validators_keypairs = types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT);
     let honest_validators: Vec<usize> = (0..HONEST_VALIDATOR_COUNT).collect();
     let adversarial_validators: Vec<usize> = (HONEST_VALIDATOR_COUNT..VALIDATOR_COUNT).collect();
-    let rig = BeaconChainHarness::new(MinimalEthSpec, None, validators_keypairs);
+    let rig = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(validators_keypairs)
+        .fresh_ephemeral_store()
+        .build();
     let (state, state_root) = rig.get_current_state_and_root();
 
     let canonical_slots_zeroth_epoch: Vec<Slot> =
@@ -1923,12 +1948,11 @@ fn finalizes_after_resuming_from_db() {
     let db_path = tempdir().unwrap();
     let store = get_store(&db_path);
 
-    let harness = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        None,
-        store.clone(),
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_disk_store(store.clone())
+        .build();
 
     harness.advance_slot();
 
@@ -1967,12 +1991,11 @@ fn finalizes_after_resuming_from_db() {
 
     let original_chain = harness.chain;
 
-    let resumed_harness = BeaconChainHarness::resume_from_disk_store(
-        MinimalEthSpec,
-        None,
-        store,
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let resumed_harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .resumed_disk_store(store)
+        .build();
 
     assert_chains_pretty_much_the_same(&original_chain, &resumed_harness.chain);
 
@@ -2037,22 +2060,20 @@ fn revert_minority_fork_on_resume() {
     // Chain with no fork epoch configured.
     let db_path1 = tempdir().unwrap();
     let store1 = get_store_with_spec(&db_path1, spec1.clone());
-    let harness1 = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        Some(spec1),
-        store1,
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness1 = BeaconChainHarness::builder(MinimalEthSpec)
+        .spec(spec1)
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_disk_store(store1)
+        .build();
 
     // Chain with fork epoch configured.
     let db_path2 = tempdir().unwrap();
     let store2 = get_store_with_spec(&db_path2, spec2.clone());
-    let harness2 = BeaconChainHarness::new_with_disk_store(
-        MinimalEthSpec,
-        Some(spec2.clone()),
-        store2,
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness2 = BeaconChainHarness::builder(MinimalEthSpec)
+        .spec(spec2.clone())
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_disk_store(store2)
+        .build();
 
     // Apply the same blocks to both chains initially.
     let mut state = harness1.get_current_state();
@@ -2130,13 +2151,12 @@ fn revert_minority_fork_on_resume() {
     // the beacon chain builder loads the head block.
     drop(harness1);
     let resume_store = get_store_with_spec(&db_path1, spec2.clone());
-    let resumed_harness = BeaconChainHarness::new_with_mutator(
-        MinimalEthSpec,
-        spec2,
-        resume_store,
-        KEYPAIRS[0..validator_count].to_vec(),
-        ChainConfig::default(),
-        |mut builder| {
+
+    let resumed_harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .spec(spec2)
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .resumed_disk_store(resume_store)
+        .override_store_mutator(Box::new(move |mut builder| {
             builder = builder
                 .resume_from_db()
                 .unwrap()
@@ -2147,8 +2167,8 @@ fn revert_minority_fork_on_resume() {
                 .unwrap()
                 .set_slot(end_slot.as_u64());
             builder
-        },
-    );
+        }))
+        .build();
 
     // Head should now be just before the fork.
     resumed_harness.chain.fork_choice().unwrap();
diff --git a/beacon_node/beacon_chain/tests/sync_committee_verification.rs b/beacon_node/beacon_chain/tests/sync_committee_verification.rs
index beeea37e62..7326a02f46 100644
--- a/beacon_node/beacon_chain/tests/sync_committee_verification.rs
+++ b/beacon_node/beacon_chain/tests/sync_committee_verification.rs
@@ -28,11 +28,11 @@ lazy_static! {
 fn get_harness(validator_count: usize) -> BeaconChainHarness<EphemeralHarnessType<E>> {
     let mut spec = E::default_spec();
     spec.altair_fork_epoch = Some(Epoch::new(0));
-    let harness = BeaconChainHarness::new(
-        MainnetEthSpec,
-        Some(spec),
-        KEYPAIRS[0..validator_count].to_vec(),
-    );
+    let harness = BeaconChainHarness::builder(MainnetEthSpec)
+        .spec(spec)
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     harness.advance_slot();
 
diff --git a/beacon_node/beacon_chain/tests/tests.rs b/beacon_node/beacon_chain/tests/tests.rs
index f4399ed374..5b85da5bf8 100644
--- a/beacon_node/beacon_chain/tests/tests.rs
+++ b/beacon_node/beacon_chain/tests/tests.rs
@@ -15,7 +15,6 @@ use operation_pool::PersistedOperationPool;
 use state_processing::{
     per_slot_processing, per_slot_processing::Error as SlotProcessingError, EpochProcessingError,
 };
-use store::config::StoreConfig;
 use types::{BeaconStateError, EthSpec, Hash256, Keypair, MinimalEthSpec, RelativeEpoch, Slot};
 
 // Should ideally be divisible by 3.
@@ -27,12 +26,11 @@ lazy_static! {
 }
 
 fn get_harness(validator_count: usize) -> BeaconChainHarness<EphemeralHarnessType<MinimalEthSpec>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        MinimalEthSpec,
-        None,
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     harness.advance_slot();
 
diff --git a/beacon_node/http_api/tests/common.rs b/beacon_node/http_api/tests/common.rs
index 04224b8471..a2298276c0 100644
--- a/beacon_node/http_api/tests/common.rs
+++ b/beacon_node/http_api/tests/common.rs
@@ -18,7 +18,7 @@ use std::net::{Ipv4Addr, SocketAddr};
 use std::sync::Arc;
 use std::time::Duration;
 use tokio::sync::{mpsc, oneshot};
-use types::{test_utils::generate_deterministic_keypairs, ChainSpec, EthSpec};
+use types::{ChainSpec, EthSpec};
 
 pub const TCP_PORT: u16 = 42;
 pub const UDP_PORT: u16 = 42;
@@ -47,11 +47,11 @@ pub struct ApiServer<E: EthSpec, SFut: Future<Output = ()>> {
 
 impl<E: EthSpec> InteractiveTester<E> {
     pub async fn new(spec: Option<ChainSpec>, validator_count: usize) -> Self {
-        let harness = BeaconChainHarness::new(
-            E::default(),
-            spec,
-            generate_deterministic_keypairs(validator_count),
-        );
+        let harness = BeaconChainHarness::builder(E::default())
+            .spec_or_default(spec)
+            .deterministic_keypairs(validator_count)
+            .fresh_ephemeral_store()
+            .build();
 
         let ApiServer {
             server,
diff --git a/beacon_node/http_api/tests/tests.rs b/beacon_node/http_api/tests/tests.rs
index 86762aeb42..df7af8cc4a 100644
--- a/beacon_node/http_api/tests/tests.rs
+++ b/beacon_node/http_api/tests/tests.rs
@@ -21,8 +21,8 @@ use tokio::sync::{mpsc, oneshot};
 use tokio::time::Duration;
 use tree_hash::TreeHash;
 use types::{
-    test_utils::generate_deterministic_keypairs, AggregateSignature, BeaconState, BitList, Domain,
-    EthSpec, Hash256, Keypair, MainnetEthSpec, RelativeEpoch, SelectionProof, SignedRoot, Slot,
+    AggregateSignature, BeaconState, BitList, Domain, EthSpec, Hash256, Keypair, MainnetEthSpec,
+    RelativeEpoch, SelectionProof, SignedRoot, Slot,
 };
 
 type E = MainnetEthSpec;
@@ -71,11 +71,11 @@ impl ApiTester {
     }
 
     pub async fn new_from_spec(spec: ChainSpec) -> Self {
-        let harness = BeaconChainHarness::new(
-            MainnetEthSpec,
-            Some(spec.clone()),
-            generate_deterministic_keypairs(VALIDATOR_COUNT),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .spec(spec.clone())
+            .deterministic_keypairs(VALIDATOR_COUNT)
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
@@ -214,11 +214,11 @@ impl ApiTester {
     }
 
     pub async fn new_from_genesis() -> Self {
-        let harness = BeaconChainHarness::new(
-            MainnetEthSpec,
-            None,
-            generate_deterministic_keypairs(VALIDATOR_COUNT),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .default_spec()
+            .deterministic_keypairs(VALIDATOR_COUNT)
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
diff --git a/beacon_node/network/src/beacon_processor/tests.rs b/beacon_node/network/src/beacon_processor/tests.rs
index 5b67d35555..de55901441 100644
--- a/beacon_node/network/src/beacon_processor/tests.rs
+++ b/beacon_node/network/src/beacon_processor/tests.rs
@@ -23,8 +23,8 @@ use std::time::Duration;
 use tokio::runtime::Runtime;
 use tokio::sync::mpsc;
 use types::{
-    test_utils::generate_deterministic_keypairs, Attestation, AttesterSlashing, EthSpec,
-    MainnetEthSpec, ProposerSlashing, SignedBeaconBlock, SignedVoluntaryExit, SubnetId,
+    Attestation, AttesterSlashing, EthSpec, MainnetEthSpec, ProposerSlashing, SignedBeaconBlock,
+    SignedVoluntaryExit, SubnetId,
 };
 
 type E = MainnetEthSpec;
@@ -75,11 +75,11 @@ impl TestRig {
         let mut spec = E::default_spec();
         spec.shard_committee_period = 2;
 
-        let harness = BeaconChainHarness::new(
-            MainnetEthSpec,
-            Some(spec),
-            generate_deterministic_keypairs(VALIDATOR_COUNT),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .spec(spec)
+            .deterministic_keypairs(VALIDATOR_COUNT)
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
diff --git a/beacon_node/network/src/service/tests.rs b/beacon_node/network/src/service/tests.rs
index db61d2a88c..f9e861a91d 100644
--- a/beacon_node/network/src/service/tests.rs
+++ b/beacon_node/network/src/service/tests.rs
@@ -9,9 +9,8 @@ mod tests {
     use sloggers::{null::NullLoggerBuilder, Build};
     use std::str::FromStr;
     use std::sync::Arc;
-    use store::config::StoreConfig;
     use tokio::runtime::Runtime;
-    use types::{test_utils::generate_deterministic_keypairs, MinimalEthSpec};
+    use types::MinimalEthSpec;
 
     fn get_logger(actual_log: bool) -> Logger {
         if actual_log {
@@ -35,13 +34,12 @@ mod tests {
     fn test_dht_persistence() {
         let log = get_logger(false);
 
-        let beacon_chain = BeaconChainHarness::new_with_store_config(
-            MinimalEthSpec,
-            None,
-            generate_deterministic_keypairs(8),
-            StoreConfig::default(),
-        )
-        .chain;
+        let beacon_chain = BeaconChainHarness::builder(MinimalEthSpec)
+            .default_spec()
+            .deterministic_keypairs(8)
+            .fresh_ephemeral_store()
+            .build()
+            .chain;
 
         let store = beacon_chain.store.clone();
 
diff --git a/beacon_node/operation_pool/src/lib.rs b/beacon_node/operation_pool/src/lib.rs
index 6609c5ac7e..dad375b32f 100644
--- a/beacon_node/operation_pool/src/lib.rs
+++ b/beacon_node/operation_pool/src/lib.rs
@@ -632,8 +632,11 @@ mod release_tests {
         validator_count: usize,
         spec: Option<ChainSpec>,
     ) -> BeaconChainHarness<EphemeralHarnessType<E>> {
-        let harness =
-            BeaconChainHarness::new(E::default(), spec, KEYPAIRS[0..validator_count].to_vec());
+        let harness = BeaconChainHarness::builder(E::default())
+            .spec_or_default(spec)
+            .keypairs(KEYPAIRS[0..validator_count].to_vec())
+            .fresh_ephemeral_store()
+            .build();
 
         harness.advance_slot();
 
diff --git a/beacon_node/store/src/iter.rs b/beacon_node/store/src/iter.rs
index 6735b4ff7d..8b11a6cc9c 100644
--- a/beacon_node/store/src/iter.rs
+++ b/beacon_node/store/src/iter.rs
@@ -371,18 +371,16 @@ mod test {
     use super::*;
     use crate::HotColdDB;
     use crate::StoreConfig as Config;
-    use beacon_chain::store::StoreConfig;
     use beacon_chain::test_utils::BeaconChainHarness;
-    use beacon_chain::types::{ChainSpec, Keypair, MainnetEthSpec};
+    use beacon_chain::types::{ChainSpec, MainnetEthSpec};
     use sloggers::{null::NullLoggerBuilder, Build};
 
     fn get_state<T: EthSpec>() -> BeaconState<T> {
-        let harness = BeaconChainHarness::new_with_store_config(
-            T::default(),
-            None,
-            vec![Keypair::random()],
-            StoreConfig::default(),
-        );
+        let harness = BeaconChainHarness::builder(T::default())
+            .default_spec()
+            .deterministic_keypairs(1)
+            .fresh_ephemeral_store()
+            .build();
         harness.advance_slot();
         harness.get_current_state()
     }
diff --git a/consensus/fork_choice/tests/tests.rs b/consensus/fork_choice/tests/tests.rs
index f299de1b6f..08b098707f 100644
--- a/consensus/fork_choice/tests/tests.rs
+++ b/consensus/fork_choice/tests/tests.rs
@@ -14,11 +14,10 @@ use fork_choice::{
     ForkChoiceStore, InvalidAttestation, InvalidBlock, QueuedAttestation,
     SAFE_SLOTS_TO_UPDATE_JUSTIFIED,
 };
-use store::{MemoryStore, StoreConfig};
+use store::MemoryStore;
 use types::{
-    test_utils::{generate_deterministic_keypair, generate_deterministic_keypairs},
-    BeaconBlock, BeaconBlockRef, BeaconState, Checkpoint, Epoch, EthSpec, Hash256,
-    IndexedAttestation, MainnetEthSpec, Slot, SubnetId,
+    test_utils::generate_deterministic_keypair, BeaconBlock, BeaconBlockRef, BeaconState,
+    Checkpoint, Epoch, EthSpec, Hash256, IndexedAttestation, MainnetEthSpec, Slot, SubnetId,
 };
 
 pub type E = MainnetEthSpec;
@@ -48,25 +47,23 @@ impl fmt::Debug for ForkChoiceTest {
 impl ForkChoiceTest {
     /// Creates a new tester.
     pub fn new() -> Self {
-        let harness = BeaconChainHarness::new_with_store_config(
-            MainnetEthSpec,
-            None,
-            generate_deterministic_keypairs(VALIDATOR_COUNT),
-            StoreConfig::default(),
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .default_spec()
+            .deterministic_keypairs(VALIDATOR_COUNT)
+            .fresh_ephemeral_store()
+            .build();
 
         Self { harness }
     }
 
     /// Creates a new tester with a custom chain config.
     pub fn new_with_chain_config(chain_config: ChainConfig) -> Self {
-        let harness = BeaconChainHarness::new_with_chain_config(
-            MainnetEthSpec,
-            None,
-            generate_deterministic_keypairs(VALIDATOR_COUNT),
-            StoreConfig::default(),
-            chain_config,
-        );
+        let harness = BeaconChainHarness::builder(MainnetEthSpec)
+            .default_spec()
+            .chain_config(chain_config)
+            .deterministic_keypairs(VALIDATOR_COUNT)
+            .fresh_ephemeral_store()
+            .build();
 
         Self { harness }
     }
diff --git a/consensus/state_processing/src/per_block_processing/tests.rs b/consensus/state_processing/src/per_block_processing/tests.rs
index fe1537a50d..78c034caac 100644
--- a/consensus/state_processing/src/per_block_processing/tests.rs
+++ b/consensus/state_processing/src/per_block_processing/tests.rs
@@ -7,7 +7,6 @@ use crate::per_block_processing::errors::{
     ProposerSlashingInvalid,
 };
 use crate::{per_block_processing::process_operations, BlockSignatureStrategy, VerifySignatures};
-use beacon_chain::store::StoreConfig;
 use beacon_chain::test_utils::{BeaconChainHarness, EphemeralHarnessType};
 use lazy_static::lazy_static;
 use ssz_types::Bitfield;
@@ -32,12 +31,11 @@ fn get_harness<E: EthSpec>(
     // Set the state and block to be in the last slot of the `epoch_offset`th epoch.
     let last_slot_of_epoch =
         (MainnetEthSpec::genesis_epoch() + epoch_offset).end_slot(E::slots_per_epoch());
-    let harness = BeaconChainHarness::new_with_store_config(
-        E::default(),
-        None,
-        KEYPAIRS[0..num_validators].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(E::default())
+        .default_spec()
+        .keypairs(KEYPAIRS[0..num_validators].to_vec())
+        .fresh_ephemeral_store()
+        .build();
     let state = harness.get_current_state();
     if last_slot_of_epoch > Slot::new(0) {
         harness.add_attested_blocks_at_slots(
diff --git a/consensus/state_processing/src/per_epoch_processing/tests.rs b/consensus/state_processing/src/per_epoch_processing/tests.rs
index ac1ce6b019..4379547bfe 100644
--- a/consensus/state_processing/src/per_epoch_processing/tests.rs
+++ b/consensus/state_processing/src/per_epoch_processing/tests.rs
@@ -1,6 +1,5 @@
 #![cfg(test)]
 use crate::per_epoch_processing::process_epoch;
-use beacon_chain::store::StoreConfig;
 use beacon_chain::test_utils::BeaconChainHarness;
 use beacon_chain::types::{EthSpec, MinimalEthSpec};
 use bls::Hash256;
@@ -11,12 +10,11 @@ use types::Slot;
 fn runs_without_error() {
     Builder::from_env(Env::default().default_filter_or("error")).init();
 
-    let harness = BeaconChainHarness::new_with_store_config(
-        MinimalEthSpec,
-        None,
-        types::test_utils::generate_deterministic_keypairs(8),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(MinimalEthSpec)
+        .default_spec()
+        .deterministic_keypairs(8)
+        .fresh_ephemeral_store()
+        .build();
     harness.advance_slot();
 
     let spec = MinimalEthSpec::default_spec();
@@ -55,11 +53,11 @@ mod release_tests {
         spec.altair_fork_epoch = Some(Epoch::new(1));
 
         let altair_state = {
-            let harness = BeaconChainHarness::new(
-                MainnetEthSpec,
-                Some(spec.clone()),
-                types::test_utils::generate_deterministic_keypairs(8),
-            );
+            let harness = BeaconChainHarness::builder(MainnetEthSpec)
+                .spec(spec.clone())
+                .deterministic_keypairs(8)
+                .fresh_ephemeral_store()
+                .build();
 
             harness.advance_slot();
 
@@ -113,11 +111,11 @@ mod release_tests {
         spec.altair_fork_epoch = None;
 
         let base_state = {
-            let harness = BeaconChainHarness::new(
-                MainnetEthSpec,
-                Some(spec.clone()),
-                types::test_utils::generate_deterministic_keypairs(8),
-            );
+            let harness = BeaconChainHarness::builder(MainnetEthSpec)
+                .spec(spec.clone())
+                .deterministic_keypairs(8)
+                .fresh_ephemeral_store()
+                .build();
 
             harness.advance_slot();
 
diff --git a/consensus/tree_hash/examples/flamegraph_beacon_state.rs b/consensus/tree_hash/examples/flamegraph_beacon_state.rs
index 309c2a2cc1..cb9fc9390a 100644
--- a/consensus/tree_hash/examples/flamegraph_beacon_state.rs
+++ b/consensus/tree_hash/examples/flamegraph_beacon_state.rs
@@ -1,4 +1,3 @@
-use beacon_chain::store::StoreConfig;
 use beacon_chain::test_utils::{BeaconChainHarness, EphemeralHarnessType};
 use types::{BeaconState, EthSpec, MainnetEthSpec};
 
@@ -6,12 +5,11 @@ const TREE_HASH_LOOPS: usize = 1_000;
 const VALIDATOR_COUNT: usize = 1_000;
 
 fn get_harness<T: EthSpec>() -> BeaconChainHarness<EphemeralHarnessType<T>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        T::default(),
-        None,
-        types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(T::default())
+        .default_spec()
+        .deterministic_keypairs(VALIDATOR_COUNT)
+        .fresh_ephemeral_store()
+        .build();
 
     harness.advance_slot();
 
diff --git a/consensus/types/src/beacon_state/committee_cache/tests.rs b/consensus/types/src/beacon_state/committee_cache/tests.rs
index f6799e0fd0..48998e26d0 100644
--- a/consensus/types/src/beacon_state/committee_cache/tests.rs
+++ b/consensus/types/src/beacon_state/committee_cache/tests.rs
@@ -1,6 +1,5 @@
 #![cfg(test)]
 use crate::test_utils::*;
-use beacon_chain::store::StoreConfig;
 use beacon_chain::test_utils::{BeaconChainHarness, EphemeralHarnessType};
 use beacon_chain::types::*;
 use swap_or_not_shuffle::shuffle_list;
@@ -13,12 +12,11 @@ lazy_static! {
 }
 
 fn get_harness<E: EthSpec>(validator_count: usize) -> BeaconChainHarness<EphemeralHarnessType<E>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        E::default(),
-        None,
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(E::default())
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
     harness.advance_slot();
     harness
 }
diff --git a/consensus/types/src/beacon_state/tests.rs b/consensus/types/src/beacon_state/tests.rs
index f8f2447aaf..d8b6c796c0 100644
--- a/consensus/types/src/beacon_state/tests.rs
+++ b/consensus/types/src/beacon_state/tests.rs
@@ -1,7 +1,6 @@
 #![cfg(test)]
 use crate::test_utils::*;
 use crate::test_utils::{SeedableRng, XorShiftRng};
-use beacon_chain::store::config::StoreConfig;
 use beacon_chain::test_utils::{
     interop_genesis_state, test_spec, BeaconChainHarness, EphemeralHarnessType,
 };
@@ -29,12 +28,11 @@ fn get_harness<E: EthSpec>(
     validator_count: usize,
     slot: Slot,
 ) -> BeaconChainHarness<EphemeralHarnessType<E>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        E::default(),
-        None,
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(E::default())
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
 
     let skip_to_slot = slot - SLOT_OFFSET;
     if skip_to_slot > Slot::new(0) {
diff --git a/testing/state_transition_vectors/src/main.rs b/testing/state_transition_vectors/src/main.rs
index 2512b03e5b..d66842e5a1 100644
--- a/testing/state_transition_vectors/src/main.rs
+++ b/testing/state_transition_vectors/src/main.rs
@@ -2,10 +2,7 @@
 mod macros;
 mod exit;
 
-use beacon_chain::{
-    store::StoreConfig,
-    test_utils::{BeaconChainHarness, EphemeralHarnessType},
-};
+use beacon_chain::test_utils::{BeaconChainHarness, EphemeralHarnessType};
 use lazy_static::lazy_static;
 use ssz::Encode;
 use std::env;
@@ -56,12 +53,11 @@ fn get_harness<E: EthSpec>(
     slot: Slot,
     validator_count: usize,
 ) -> BeaconChainHarness<EphemeralHarnessType<E>> {
-    let harness = BeaconChainHarness::new_with_store_config(
-        E::default(),
-        None,
-        KEYPAIRS[0..validator_count].to_vec(),
-        StoreConfig::default(),
-    );
+    let harness = BeaconChainHarness::builder(E::default())
+        .default_spec()
+        .keypairs(KEYPAIRS[0..validator_count].to_vec())
+        .fresh_ephemeral_store()
+        .build();
     let skip_to_slot = slot - SLOT_OFFSET;
     if skip_to_slot > Slot::new(0) {
         let state = harness.get_current_state();