Add BeaconChainHarness tests for The Merge (#2661)

* Start adding merge tests

* Expose MockExecutionLayer

* Add mock_execution_layer to BeaconChainHarness

* Progress with merge test

* Return more detailed errors with gas limit issues

* Use a better gas limit in block gen

* Ensure TTD is met in block gen

* Fix basic_merge tests

* Start geth testing

* Fix conflicts after rebase

* Remove geth tests

* Improve merge test

* Address clippy lints

* Make pow block gen a pure function

* Add working new test, breaking existing test

* Fix test names

* Add should_panic

* Don't run merge tests in debug

* Detect a tokio runtime when starting MockServer

* Fix clippy lint, include merge tests

consensus/state_processing/src/per_block_processing.rs

@@ -296,13 +296,16 @@ pub fn get_new_eth1_data<T: EthSpec>(
 }
 
 /// https://github.com/ethereum/consensus-specs/blob/dev/specs/merge/beacon-chain.md#is_valid_gas_limit
-pub fn is_valid_gas_limit<T: EthSpec>(
+pub fn verify_is_valid_gas_limit<T: EthSpec>(
     payload: &ExecutionPayload<T>,
     parent: &ExecutionPayloadHeader<T>,
-) -> Result<bool, ArithError> {
+) -> Result<(), BlockProcessingError> {
     // check if payload used too much gas
     if payload.gas_used > payload.gas_limit {
-        return Ok(false);
+        return Err(BlockProcessingError::ExecutionInvalidGasLimit {
+            used: payload.gas_used,
+            limit: payload.gas_limit,
+        });
     }
     // check if payload changed the gas limit too much
     if payload.gas_limit
@@ -310,21 +313,30 @@ pub fn is_valid_gas_limit<T: EthSpec>(
             .gas_limit
             .safe_add(parent.gas_limit.safe_div(T::gas_limit_denominator())?)?
     {
-        return Ok(false);
+        return Err(BlockProcessingError::ExecutionInvalidGasLimitIncrease {
+            limit: payload.gas_limit,
+            parent_limit: parent.gas_limit,
+        });
     }
     if payload.gas_limit
         <= parent
             .gas_limit
             .safe_sub(parent.gas_limit.safe_div(T::gas_limit_denominator())?)?
     {
-        return Ok(false);
+        return Err(BlockProcessingError::ExecutionInvalidGasLimitDecrease {
+            limit: payload.gas_limit,
+            parent_limit: parent.gas_limit,
+        });
     }
     // check if the gas limit is at least the minimum gas limit
     if payload.gas_limit < T::min_gas_limit() {
-        return Ok(false);
+        return Err(BlockProcessingError::ExecutionInvalidGasLimitTooSmall {
+            limit: payload.gas_limit,
+            min: T::min_gas_limit(),
+        });
     }
 
-    Ok(true)
+    Ok(())
 }
 
 /// https://github.com/ethereum/consensus-specs/blob/dev/specs/merge/beacon-chain.md#process_execution_payload
@@ -355,13 +367,7 @@ pub fn process_execution_payload<T: EthSpec>(
                 found: payload.block_number,
             }
         );
-        block_verify!(
-            is_valid_gas_limit(payload, state.latest_execution_payload_header()?)?,
-            BlockProcessingError::ExecutionInvalidGasLimit {
-                used: payload.gas_used,
-                limit: payload.gas_limit,
-            }
-        );
+        verify_is_valid_gas_limit(payload, state.latest_execution_payload_header()?)?;
     }
     block_verify!(
         payload.random == *state.get_randao_mix(state.current_epoch())?,

consensus/state_processing/src/per_block_processing/errors.rs

@@ -73,6 +73,18 @@ pub enum BlockProcessingError {
         used: u64,
         limit: u64,
     },
+    ExecutionInvalidGasLimitIncrease {
+        limit: u64,
+        parent_limit: u64,
+    },
+    ExecutionInvalidGasLimitDecrease {
+        limit: u64,
+        parent_limit: u64,
+    },
+    ExecutionInvalidGasLimitTooSmall {
+        limit: u64,
+        min: u64,
+    },
     ExecutionInvalidTimestamp {
         expected: u64,
         found: u64,