Allow TaskExecutor to be used in async tests (#3178)

# Description

Since the `TaskExecutor` currently requires a `Weak<Runtime>`, it's impossible to use it in an async test where the `Runtime` is created outside our scope. Whilst we *could* create a new `Runtime` instance inside the async test, dropping that `Runtime` would cause a panic (you can't drop a `Runtime` in an async context).

To address this issue, this PR creates the `enum Handle`, which supports either:

- A `Weak<Runtime>` (for use in our production code)
- A `Handle` to a runtime (for use in testing)

In theory, there should be no change to the behaviour of our production code (beyond some slightly different descriptions in HTTP 500 errors), or even our tests. If there is no change, you might ask *"why bother?"*. There are two PRs (#3070 and #3175) that are waiting on these fixes to introduce some new tests. Since we've added the EL to the `BeaconChain` (for the merge), we are now doing more async stuff in tests.

I've also added a `RuntimeExecutor` to the `BeaconChainTestHarness`. Whilst that's not immediately useful, it will become useful in the near future with all the new async testing.

beacon_node/beacon_chain/src/test_utils.rs

@@ -12,15 +12,12 @@ use crate::{
 };
 use bls::get_withdrawal_credentials;
 use execution_layer::{
-    test_utils::{
-        ExecutionBlockGenerator, ExecutionLayerRuntime, MockExecutionLayer, DEFAULT_TERMINAL_BLOCK,
-    },
+    test_utils::{ExecutionBlockGenerator, MockExecutionLayer, DEFAULT_TERMINAL_BLOCK},
     ExecutionLayer,
 };
 use futures::channel::mpsc::Receiver;
 pub use genesis::{interop_genesis_state, DEFAULT_ETH1_BLOCK_HASH};
 use int_to_bytes::int_to_bytes32;
-use logging::test_logger;
 use merkle_proof::MerkleTree;
 use parking_lot::Mutex;
 use parking_lot::RwLockWriteGuard;
@@ -41,7 +38,7 @@ use std::str::FromStr;
 use std::sync::Arc;
 use std::time::Duration;
 use store::{config::StoreConfig, HotColdDB, ItemStore, LevelDB, MemoryStore};
-use task_executor::ShutdownReason;
+use task_executor::{test_utils::TestRuntime, ShutdownReason};
 use tree_hash::TreeHash;
 use types::sync_selection_proof::SyncSelectionProof;
 pub use types::test_utils::generate_deterministic_keypairs;
@@ -151,8 +148,8 @@ pub struct Builder<T: BeaconChainTypes> {
     initial_mutator: Option<BoxedMutator<T::EthSpec, T::HotStore, T::ColdStore>>,
     store_mutator: Option<BoxedMutator<T::EthSpec, T::HotStore, T::ColdStore>>,
     execution_layer: Option<ExecutionLayer>,
-    execution_layer_runtime: Option<ExecutionLayerRuntime>,
     mock_execution_layer: Option<MockExecutionLayer<T::EthSpec>>,
+    runtime: TestRuntime,
     log: Logger,
 }
 
@@ -255,6 +252,9 @@ where
     Cold: ItemStore<E>,
 {
     pub fn new(eth_spec_instance: E) -> Self {
+        let runtime = TestRuntime::default();
+        let log = runtime.log.clone();
+
         Self {
             eth_spec_instance,
             spec: None,
@@ -266,8 +266,8 @@ where
             store_mutator: None,
             execution_layer: None,
             mock_execution_layer: None,
-            execution_layer_runtime: None,
-            log: test_logger(),
+            runtime,
+            log,
         }
     }
 
@@ -330,8 +330,6 @@ where
             "execution layer already defined"
         );
 
-        let el_runtime = ExecutionLayerRuntime::default();
-
         let urls: Vec<SensitiveUrl> = urls
             .iter()
             .map(|s| SensitiveUrl::parse(*s))
@@ -346,19 +344,19 @@ where
         };
         let execution_layer = ExecutionLayer::from_config(
             config,
-            el_runtime.task_executor.clone(),
-            el_runtime.log.clone(),
+            self.runtime.task_executor.clone(),
+            self.log.clone(),
         )
         .unwrap();
 
         self.execution_layer = Some(execution_layer);
-        self.execution_layer_runtime = Some(el_runtime);
         self
     }
 
     pub fn mock_execution_layer(mut self) -> Self {
         let spec = self.spec.clone().expect("cannot build without spec");
         let mock = MockExecutionLayer::new(
+            self.runtime.task_executor.clone(),
             spec.terminal_total_difficulty,
             DEFAULT_TERMINAL_BLOCK,
             spec.terminal_block_hash,
@@ -383,7 +381,7 @@ where
     pub fn build(self) -> BeaconChainHarness<BaseHarnessType<E, Hot, Cold>> {
         let (shutdown_tx, shutdown_receiver) = futures::channel::mpsc::channel(1);
 
-        let log = test_logger();
+        let log = self.log;
         let spec = self.spec.expect("cannot build without spec");
         let seconds_per_slot = spec.seconds_per_slot;
         let validator_keypairs = self
@@ -395,6 +393,7 @@ where
             .custom_spec(spec)
             .store(self.store.expect("cannot build without store"))
             .store_migrator_config(MigratorConfig::default().blocking())
+            .task_executor(self.runtime.task_executor.clone())
             .execution_layer(self.execution_layer)
             .dummy_eth1_backend()
             .expect("should build dummy backend")
@@ -434,8 +433,8 @@ where
             chain: Arc::new(chain),
             validator_keypairs,
             shutdown_receiver: Arc::new(Mutex::new(shutdown_receiver)),
+            runtime: self.runtime,
             mock_execution_layer: self.mock_execution_layer,
-            execution_layer_runtime: self.execution_layer_runtime,
             rng: make_rng(),
         }
     }
@@ -451,9 +450,9 @@ pub struct BeaconChainHarness<T: BeaconChainTypes> {
     pub chain: Arc<BeaconChain<T>>,
     pub spec: ChainSpec,
     pub shutdown_receiver: Arc<Mutex<Receiver<ShutdownReason>>>,
+    pub runtime: TestRuntime,
 
     pub mock_execution_layer: Option<MockExecutionLayer<T::EthSpec>>,
-    pub execution_layer_runtime: Option<ExecutionLayerRuntime>,
 
     pub rng: Mutex<StdRng>,
 }