Add echo test for server

tests/test_server.cpp

@@ -0,0 +1,61 @@
+#include "config.hpp"
+#include "connection.hpp"
+#include "connection_handler.hpp"
+#include "server.hpp"
+
+#include <doctest/doctest.h>
+#include <future>
+#include <string_view>
+#include <thread>
+
+// Helper to copy a string into arena memory
+static std::string_view arena_copy_string(std::string_view str, Arena &arena) {
+  if (str.empty()) {
+    return std::string_view{};
+  }
+  char *copied = arena.allocate<char>(str.size());
+  std::memcpy(copied, str.data(), str.size());
+  return std::string_view(copied, str.size());
+}
+
+struct EchoHandler : ConnectionHandler {
+  std::future<void> f;
+  void on_data_arrived(std::string_view data, Connection &conn) override {
+    Arena arena;
+    auto reply = std::span{arena.allocate<std::string_view>(1), 1};
+    reply[0] = arena_copy_string(data, arena);
+    f = std::async(std::launch::async, [wconn = conn.get_weak_ref(), reply,
+                                        arena = std::move(arena)]() mutable {
+      if (auto conn = wconn.lock()) {
+        conn->append_message(reply, std::move(arena));
+      } else {
+        REQUIRE(false);
+      }
+    });
+  }
+};
+
+TEST_CASE("Echo test") {
+  EchoHandler handler;
+  weaseldb::Config config;
+  config.server.io_threads = 1;
+  auto server = Server::create(config, handler, {});
+  int fd = server->create_local_connection();
+
+  auto runThread = std::thread{[&]() { server->run(); }};
+
+  SUBCASE("writes hello back") {
+    int w = write(fd, "hello", 5);
+    REQUIRE(w == 5);
+    char buf[6];
+    buf[5] = 0;
+    int r = read(fd, buf, 5);
+    REQUIRE(r == 5);
+    CHECK(std::string(buf) == "hello");
+  }
+
+  close(fd);
+
+  server->shutdown();
+  runThread.join();
+}