Add Nethermind integration tests (#3100)

## Proposed Changes

Extend the current Geth merge integration tests to support Nethermind.

testing/execution_engine_integration/src/nethermind.rs

@@ -0,0 +1,117 @@
+use crate::build_utils;
+use crate::execution_engine::GenericExecutionEngine;
+use crate::genesis_json::nethermind_genesis_json;
+use std::path::{Path, PathBuf};
+use std::process::{Child, Command, Output};
+use std::{env, fs::File};
+use tempfile::TempDir;
+use unused_port::unused_tcp_port;
+
+const NETHERMIND_BRANCH: &str = "kiln";
+const NETHERMIND_REPO_URL: &str = "https://github.com/NethermindEth/nethermind";
+
+fn build_result(repo_dir: &Path) -> Output {
+    Command::new("dotnet")
+        .arg("build")
+        .arg("src/Nethermind/Nethermind.sln")
+        .arg("-c")
+        .arg("Release")
+        .current_dir(repo_dir)
+        .output()
+        .expect("failed to make nethermind")
+}
+
+pub fn build(execution_clients_dir: &Path) {
+    let repo_dir = execution_clients_dir.join("nethermind");
+
+    if !repo_dir.exists() {
+        // Clone the repo
+        assert!(build_utils::clone_repo(
+            execution_clients_dir,
+            NETHERMIND_REPO_URL
+        ));
+    }
+
+    // Checkout the correct branch
+    assert!(build_utils::checkout_branch(&repo_dir, NETHERMIND_BRANCH));
+
+    // Update the branch
+    assert!(build_utils::update_branch(&repo_dir, NETHERMIND_BRANCH));
+
+    // Build nethermind
+    build_utils::check_command_output(build_result(&repo_dir), "dotnet build failed");
+
+    // Build nethermind a second time to enable Merge-related features.
+    // Not sure why this is necessary.
+    build_utils::check_command_output(build_result(&repo_dir), "dotnet build failed");
+}
+
+/*
+ * Nethermind-specific Implementation for GenericExecutionEngine
+ */
+
+#[derive(Clone)]
+pub struct NethermindEngine;
+
+impl NethermindEngine {
+    fn binary_path() -> PathBuf {
+        let manifest_dir: PathBuf = env::var("CARGO_MANIFEST_DIR").unwrap().into();
+        manifest_dir
+            .join("execution_clients")
+            .join("nethermind")
+            .join("src")
+            .join("Nethermind")
+            .join("Nethermind.Runner")
+            .join("bin")
+            .join("Release")
+            .join("net6.0")
+            .join("Nethermind.Runner")
+    }
+}
+
+impl GenericExecutionEngine for NethermindEngine {
+    fn init_datadir() -> TempDir {
+        let datadir = TempDir::new().unwrap();
+
+        let genesis_json_path = datadir.path().join("genesis.json");
+        let mut file = File::create(&genesis_json_path).unwrap();
+        let json = nethermind_genesis_json();
+        serde_json::to_writer(&mut file, &json).unwrap();
+
+        datadir
+    }
+
+    fn start_client(
+        datadir: &TempDir,
+        http_port: u16,
+        http_auth_port: u16,
+        jwt_secret_path: PathBuf,
+    ) -> Child {
+        let network_port = unused_tcp_port().unwrap();
+        let genesis_json_path = datadir.path().join("genesis.json");
+
+        Command::new(Self::binary_path())
+            .arg("--datadir")
+            .arg(datadir.path().to_str().unwrap())
+            .arg("--config")
+            .arg("themerge_kiln_testvectors")
+            .arg("--Init.ChainSpecPath")
+            .arg(genesis_json_path.to_str().unwrap())
+            .arg("--JsonRpc.AdditionalRpcUrls")
+            .arg(format!("http://localhost:{}|http;ws|net;eth;subscribe;engine;web3;client|no-auth,http://localhost:{}|http;ws|net;eth;subscribe;engine;web3;client", http_port, http_auth_port))
+            .arg("--JsonRpc.EnabledModules")
+            .arg("net,eth,subscribe,web3,admin,engine")
+            .arg("--JsonRpc.Port")
+            .arg(http_port.to_string())
+            .arg("--Network.DiscoveryPort")
+            .arg(network_port.to_string())
+            .arg("--Network.P2PPort")
+            .arg(network_port.to_string())
+            .arg("--JsonRpc.JwtSecretFile")
+            .arg(jwt_secret_path.as_path().to_str().unwrap())
+            .stdout(build_utils::build_stdio())
+            .stderr(build_utils::build_stdio())
+            .spawn()
+            .expect("failed to start nethermind")
+    }
+}