Kintsugi on_merge_block tests (#2811)

* Start v1.1.5 updates

* Implement new payload creation logic

* Tidy, add comments

* Remove unused error enums

* Add validate payload for gossip

* Refactor validate_merge_block

* Split payload verification in per block processing

* Add execute_payload

* Tidy

* Tidy

* Start working on new fork choice tests

* Fix failing merge block test

* Skip block_lookup_failed test

* Fix failing terminal block test

* Fixes from self-review

* Address review comments

testing/ef_tests/src/handler.rs

@@ -491,6 +491,34 @@ impl<E: EthSpec + TypeName> Handler for ForkChoiceOnBlockHandler<E> {
     }
 }
 
+#[derive(Derivative)]
+#[derivative(Default(bound = ""))]
+pub struct ForkChoiceOnMergeBlockHandler<E>(PhantomData<E>);
+
+impl<E: EthSpec + TypeName> Handler for ForkChoiceOnMergeBlockHandler<E> {
+    type Case = cases::ForkChoiceTest<E>;
+
+    fn config_name() -> &'static str {
+        E::name()
+    }
+
+    fn runner_name() -> &'static str {
+        "fork_choice"
+    }
+
+    fn handler_name(&self) -> String {
+        "on_merge_block".into()
+    }
+
+    fn is_enabled_for_fork(&self, fork_name: ForkName) -> bool {
+        // These tests check block validity (which may include signatures) and there is no need to
+        // run them with fake crypto.
+        cfg!(not(feature = "fake_crypto"))
+            // These tests only exist for the merge.
+            && fork_name == ForkName::Merge
+    }
+}
+
 #[derive(Derivative)]
 #[derivative(Default(bound = ""))]
 pub struct GenesisValidityHandler<E>(PhantomData<E>);