Add first changes to syncing logic

- Adds testing framework
- Breaks out new `NetworkContext` object

beacon_node/beacon_chain/src/test_utils/mod.rs

@@ -0,0 +1,3 @@
+mod testing_beacon_chain_builder;
+
+pub use testing_beacon_chain_builder::TestingBeaconChainBuilder;

beacon_node/beacon_chain/src/test_utils/testing_beacon_chain_builder.rs

@@ -0,0 +1,50 @@
+pub use crate::{BeaconChain, BeaconChainError, CheckPoint};
+use db::{
+    stores::{BeaconBlockStore, BeaconStateStore},
+    MemoryDB,
+};
+use fork_choice::BitwiseLMDGhost;
+use slot_clock::TestingSlotClock;
+use ssz::TreeHash;
+use std::sync::Arc;
+use types::test_utils::TestingBeaconStateBuilder;
+use types::*;
+
+type TestingBeaconChain = BeaconChain<MemoryDB, TestingSlotClock, BitwiseLMDGhost<MemoryDB>>;
+
+pub struct TestingBeaconChainBuilder {
+    state_builder: TestingBeaconStateBuilder,
+}
+
+impl TestingBeaconChainBuilder {
+    pub fn build(self, spec: &ChainSpec) -> TestingBeaconChain {
+        let db = Arc::new(MemoryDB::open());
+        let block_store = Arc::new(BeaconBlockStore::new(db.clone()));
+        let state_store = Arc::new(BeaconStateStore::new(db.clone()));
+        let slot_clock = TestingSlotClock::new(spec.genesis_slot.as_u64());
+        let fork_choice = BitwiseLMDGhost::new(block_store.clone(), state_store.clone());
+
+        let (genesis_state, _keypairs) = self.state_builder.build();
+
+        let mut genesis_block = BeaconBlock::empty(&spec);
+        genesis_block.state_root = Hash256::from_slice(&genesis_state.hash_tree_root());
+
+        // Create the Beacon Chain
+        BeaconChain::from_genesis(
+            state_store.clone(),
+            block_store.clone(),
+            slot_clock,
+            genesis_state,
+            genesis_block,
+            spec.clone(),
+            fork_choice,
+        )
+        .unwrap()
+    }
+}
+
+impl From<TestingBeaconStateBuilder> for TestingBeaconChainBuilder {
+    fn from(state_builder: TestingBeaconStateBuilder) -> TestingBeaconChainBuilder {
+        TestingBeaconChainBuilder { state_builder }
+    }
+}