Add integration tests based on testcontainers

tests/containers/alpine/runtime-check.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+set -eu
+
+command -v wg >/dev/null
+command -v ip >/dev/null
+command -v busybox >/dev/null
+wg --version >/dev/null
+ip -Version >/dev/null
+ip link show lo >/dev/null
+
+if [ "${1:-}" = "--driver" ]; then
+    shift
+    [ "$#" -eq 1 ]
+    [ -x "$1" ]
+    # M8.4 provides this ignored cfg(test) entry point. Keep the selection
+    # exact so no other ignored test can run in the fixture image.
+    "$1" --ignored --exact container_driver::alpine_readiness --test-threads=1
+elif [ "$#" -ne 0 ]; then
+    echo "usage: wireguard-admin-alpine-check [--driver PATH]" >&2
+    exit 2
+fi