diff --git a/lighthouse/state/block/validation/tests.rs b/lighthouse/state/block/validation/tests.rs
index b2584b677..e5522e37f 100644
--- a/lighthouse/state/block/validation/tests.rs
+++ b/lighthouse/state/block/validation/tests.rs
@@ -6,6 +6,7 @@ use self::ssz::{
 use std::sync::Arc;
 use super::{
     validate_ssz_block,
+    SszBlockValidationError,
     BlockStatus,
     AttesterMap,
     ProposerMap,
@@ -54,162 +55,267 @@ impl TestStore {
     }
 }
 
-pub fn generate_attestations_for_slot(attestation_slot: u64,
-                                  block_slot: u64,
-                                  shard_count: u16,
-                                  validators_per_shard: usize,
-                                  cycle_length: u8,
-                                  parent_hashes: &[Hash256],
-                                  shard_block_hash: &Hash256,
-                                  justified_block_hash: &Hash256,
-                                  justified_slot: u64,
-                                  stores: &TestStore)
-    -> (AttesterMap, Vec<AttestationRecord>, Vec<Keypair>)
-{
-    let mut i = 0;
-    let mut attester_map = AttesterMap::new();
-    let mut attestations = vec![];
-    let mut keypairs = vec![];
-    for shard in 0..shard_count {
-        let mut attesters = vec![];
-        let mut attester_bitfield = Bitfield::new();
-        let mut aggregate_sig = AggregateSignature::new();
-
-        let parent_hashes_slice = {
-            let distance: usize = (block_slot - attestation_slot) as usize;
-            let last: usize = parent_hashes.len() - distance;
-            let first: usize = last - usize::from(cycle_length);
-            &parent_hashes[first..last]
-        };
-
-        let attestation_message = {
-            let mut stream = SszStream::new();
-            stream.append(&attestation_slot);
-            stream.append_vec(&parent_hashes_slice.to_vec());
-            stream.append(&shard);
-            stream.append(shard_block_hash);
-            stream.append(&justified_slot);
-            let bytes = stream.drain();
-            canonical_hash(&bytes)
-        };
-
-
-
-        for attestation_index in 0..validators_per_shard {
-           /*
-            * Add the attester to the attestation indices for this shard.
-            */
-           attesters.push(i);
-           /*
-            * Set the voters bit on the bitfield to true.
-            */
-           attester_bitfield.set_bit(attestation_index, true);
-           /*
-            * Generate a random keypair for this validatior and clone it into the
-            * list of keypairs.
-            */
-           let keypair = Keypair::random();
-           keypairs.push(keypair.clone());
-           /*
-            * Store the validators public key in the database.
-            */
-           stores.validator.put_public_key_by_index(i, &keypair.pk).unwrap();
-           /*
-            * Generate a new signature and aggregate it on the rolling signature.
-            */
-           let sig = Signature::new(&attestation_message, &keypair.sk);
-           aggregate_sig.add(&sig);
-           /*
-            * Increment the validator counter to monotonically assign validators.
-            */
-           i += 1;
-        }
-
-        attester_map.insert((attestation_slot, shard), attesters);
-        let attestation = AttestationRecord {
-            slot: attestation_slot,
-            shard_id: shard,
-            oblique_parent_hashes: vec![],
-            shard_block_hash: *shard_block_hash,
-            attester_bitfield,
-            justified_slot,
-            justified_block_hash: *justified_block_hash,
-            aggregate_sig,
-        };
-        attestations.push(attestation);
-    }
-    (attester_map, attestations, keypairs)
+#[derive(Debug)]
+pub struct TestParams {
+    pub total_validators: usize,
+    pub cycle_length: u8,
+    pub shard_count: u16,
+    pub shards_per_slot: u16,
+    pub validators_per_shard: usize,
+    pub block_slot: u64,
+    pub attestations_justified_slot: u64,
 }
+type ParentHashes = Vec<Hash256>;
 
-#[test]
-fn test_block_validation() {
+/// Setup for a block validation function, without actually executing the
+/// block validation function.
+pub fn setup_block_validation_scenario(params: &TestParams)
+    -> (Block, ParentHashes, AttesterMap, ProposerMap, TestStore)
+{
     let stores = TestStore::new();
 
-    let cycle_length: u8 = 2;
-    let shard_count: u16 = 2;
-    let present_slot = u64::from(cycle_length) * 10000;
-    let justified_slot = present_slot - u64::from(cycle_length);
-    let justified_block_hash = Hash256::from("justified_hash".as_bytes());
-    let shard_block_hash = Hash256::from("shard_hash".as_bytes());
+    let cycle_length = params.cycle_length;
+    let shards_per_slot = params.shards_per_slot;
+    let validators_per_shard = params.validators_per_shard;
+    let block_slot = params.block_slot;
+    let attestations_justified_slot = params.attestations_justified_slot;
+
     let parent_hashes: Vec<Hash256> = (0..(cycle_length * 2))
         .map(|i| Hash256::from(i as u64))
         .collect();
+    let parent_hash = Hash256::from("parent_hash".as_bytes());
+    let randao_reveal = Hash256::from("randao_reveal".as_bytes());
+    let justified_block_hash = Hash256::from("justified_hash".as_bytes());
     let pow_chain_ref = Hash256::from("pow_chain".as_bytes());
     let active_state_root = Hash256::from("active_state".as_bytes());
     let crystallized_state_root = Hash256::from("cry_state".as_bytes());
+    let shard_block_hash = Hash256::from("shard_block_hash".as_bytes());
 
     stores.pow_chain.put_block_hash(pow_chain_ref.as_ref()).unwrap();
     stores.block.put_block(justified_block_hash.as_ref(), &vec![42]).unwrap();
 
-    let validators_per_shard = 10;
-
-    let block_slot = present_slot;
     let validator_index: usize = 0;
     let proposer_map = {
         let mut proposer_map = ProposerMap::new();
-        proposer_map.insert(present_slot, validator_index);
+        proposer_map.insert(block_slot, validator_index);
         proposer_map
     };
+    /*
     let attestation_slot = block_slot - 1;
     let (attester_map, attestations, _keypairs) =
         generate_attestations_for_slot(
             attestation_slot,
             block_slot,
-            shard_count,
+            shards_per_slot,
             validators_per_shard,
             cycle_length,
             &parent_hashes,
-            &shard_block_hash,
+            &Hash256::from("shard_hash".as_bytes()),
             &justified_block_hash,
-            justified_slot,
+            attestations_justified_slot,
             &stores);
+    */
+    let (attester_map, attestations, _keypairs) = {
+        let mut i = 0;
+        let attestation_slot = block_slot - 1;
+        let mut attester_map = AttesterMap::new();
+        let mut attestations = vec![];
+        let mut keypairs = vec![];
+        for shard in 0..shards_per_slot {
+            let mut attesters = vec![];
+            let mut attester_bitfield = Bitfield::new();
+            let mut aggregate_sig = AggregateSignature::new();
+
+            let parent_hashes_slice = {
+                let distance: usize = (block_slot - attestation_slot) as usize;
+                let last: usize = parent_hashes.len() - distance;
+                let first: usize = last - usize::from(cycle_length);
+                &parent_hashes[first..last]
+            };
+
+            let attestation_message = {
+                let mut stream = SszStream::new();
+                stream.append(&attestation_slot);
+                stream.append_vec(&parent_hashes_slice.to_vec());
+                stream.append(&shard);
+                stream.append(&shard_block_hash);
+                stream.append(&attestations_justified_slot);
+                let bytes = stream.drain();
+                canonical_hash(&bytes)
+            };
+
+
+
+            for attestation_index in 0..validators_per_shard {
+               /*
+                * Add the attester to the attestation indices for this shard.
+                */
+               attesters.push(i);
+               /*
+                * Set the voters bit on the bitfield to true.
+                */
+               attester_bitfield.set_bit(attestation_index, true);
+               /*
+                * Generate a random keypair for this validatior and clone it into the
+                * list of keypairs.
+                */
+               let keypair = Keypair::random();
+               keypairs.push(keypair.clone());
+               /*
+                * Store the validators public key in the database.
+                */
+               stores.validator.put_public_key_by_index(i, &keypair.pk).unwrap();
+               /*
+                * Generate a new signature and aggregate it on the rolling signature.
+                */
+               let sig = Signature::new(&attestation_message, &keypair.sk);
+               aggregate_sig.add(&sig);
+               /*
+                * Increment the validator counter to monotonically assign validators.
+                */
+               i += 1;
+            }
+
+            attester_map.insert((attestation_slot, shard), attesters);
+            let attestation = AttestationRecord {
+                slot: attestation_slot,
+                shard_id: shard,
+                oblique_parent_hashes: vec![],
+                shard_block_hash,
+                attester_bitfield,
+                justified_slot: attestations_justified_slot,
+                justified_block_hash,
+                aggregate_sig,
+            };
+            attestations.push(attestation);
+        }
+        (attester_map, attestations, keypairs)
+    };
 
     let block = Block {
-        parent_hash: Hash256::from("parent".as_bytes()),
+        parent_hash,
         slot_number: block_slot,
-        randao_reveal: Hash256::from("randao".as_bytes()),
+        randao_reveal,
         attestations,
         pow_chain_ref,
         active_state_root,
         crystallized_state_root,
     };
 
-    let mut stream = SszStream::new();
-    stream.append(&block);
-    let serialized_block = stream.drain();
-    let ssz_block = SszBlock::from_slice(&serialized_block[..]).unwrap();
+    (block,
+     parent_hashes,
+     attester_map,
+     proposer_map,
+     stores)
+}
 
-    let status = validate_ssz_block(
+/// Helper function to take some Block and SSZ serialize it.
+pub fn serialize_block(b: &Block) -> Vec<u8> {
+    let mut stream = SszStream::new();
+    stream.append(b);
+    stream.drain()
+}
+
+/// Setup and run a block validation scenario, given some parameters.
+///
+/// Returns the Result returned from the block validation function.
+pub fn run_block_validation_scenario<F>(
+    validation_slot: u64,
+    validation_last_justified_slot: u64,
+    params: &TestParams,
+    mutator_func: F)
+    -> Result<BlockStatus, SszBlockValidationError>
+    where F: FnOnce(Block, AttesterMap, ProposerMap, TestStore)
+                -> (Block, AttesterMap, ProposerMap, TestStore)
+{
+    let (block,
+     parent_hashes,
+     attester_map,
+     proposer_map,
+     stores) = setup_block_validation_scenario(&params);
+
+    let (block,
+         attester_map,
+         proposer_map,
+         stores) = mutator_func(block, attester_map, proposer_map, stores);
+
+    let ssz_bytes = serialize_block(&block);
+    let ssz_block = SszBlock::from_slice(&ssz_bytes[..])
+        .unwrap();
+
+    validate_ssz_block(
         &ssz_block,
-        present_slot,
-        cycle_length,
-        justified_slot,
+        validation_slot,
+        params.cycle_length,
+        validation_last_justified_slot,
         &Arc::new(parent_hashes),
         &Arc::new(proposer_map),
         &Arc::new(attester_map),
         &stores.block.clone(),
         &stores.validator.clone(),
-        &stores.pow_chain.clone()).unwrap();
-
-    assert_eq!(status, BlockStatus::NewBlock);
+        &stores.pow_chain.clone())
+}
+
+fn get_simple_params() -> TestParams {
+    let validators_per_shard: usize = 5;
+    let cycle_length: u8 = 2;
+    let shard_count: u16 = 4;
+    let shards_per_slot: u16 = shard_count / u16::from(cycle_length);
+    let total_validators: usize = validators_per_shard * shard_count as usize;
+    let block_slot = u64::from(cycle_length) * 10000;
+    let attestations_justified_slot = block_slot - u64::from(cycle_length);
+
+    TestParams {
+        total_validators,
+        cycle_length,
+        shard_count,
+        shards_per_slot,
+        validators_per_shard,
+        block_slot,
+        attestations_justified_slot,
+    }
+}
+
+#[test]
+fn test_block_validation_simple_scenario_valid() {
+    let params = get_simple_params();
+
+    let validation_slot = params.block_slot;
+    let validation_last_justified_slot = params.attestations_justified_slot;
+
+    let no_mutate = |block, attester_map, proposer_map, stores| {
+        (block, attester_map, proposer_map, stores)
+    };
+
+    let status = run_block_validation_scenario(
+        validation_slot,
+        validation_last_justified_slot,
+        &params,
+        no_mutate);
+
+    assert_eq!(status.unwrap(), BlockStatus::NewBlock);
+}
+
+#[test]
+fn test_block_validation_simple_scenario_invalid_2nd_attestation() {
+    let params = get_simple_params();
+
+    let validation_slot = params.block_slot;
+    let validation_last_justified_slot = params.attestations_justified_slot;
+
+    let mutator = |mut block: Block, attester_map, proposer_map, stores| {
+        /*
+         * Set the second attestaion record to have an invalid signature.
+         */
+        block.attestations[1].aggregate_sig = AggregateSignature::new();
+        (block, attester_map, proposer_map, stores)
+    };
+
+    let status = run_block_validation_scenario(
+        validation_slot,
+        validation_last_justified_slot,
+        &params,
+        mutator);
+
+    assert_eq!(status, Err(SszBlockValidationError::AttestationSignatureFailed));
 }