added test infrastructure based on docker/podman

* documentation added
* scripts to setup image and start container added

post_installation_script_test/Dockerfile

@@ -0,0 +1,41 @@
+FROM ubuntu:22.04
+
+# Minimal image for safe simulation of apt installs.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    bash wget tar curl gnupg ca-certificates apt-utils apt coreutils file procps && \
+    apt-get clean && rm -rf /var/lib/apt/lists/*
+
+# sudo wrapper: simulate apt installs and avoid making changes to the image
+RUN cat > /usr/local/bin/sudo <<'EOF'
+#!/bin/sh
+# sudo wrapper for simulation:
+# - simulate installs with `apt-get -s install ...`
+# - run `apt-get update` quietly (needed so apt -s has metadata)
+# - otherwise echo the command (no-op)
+cmd="$1"
+arg2="${2:-}"
+if [ "$cmd" = "apt" ] || [ "$cmd" = "apt-get" ]; then
+  if [ "$arg2" = "install" ]; then
+    shift 2
+    echo "[sudo-wrapper] simulating: apt-get -s install $@"
+    apt-get -s install "$@"
+    exit $?
+  elif [ "$arg2" = "update" ]; then
+    # do not run update at runtime (may require extra privileges); simulate instead
+    echo "[sudo-wrapper] simulating: apt-get update (no-op in container)"
+    exit 0
+  else
+    echo "[sudo-wrapper] would run: $@"
+    exit 0
+  fi
+else
+  echo "[sudo-wrapper] would run: $@"
+  exit 0
+fi
+EOF
+RUN chmod +x /usr/local/bin/sudo
+
+ENV PATH=/usr/local/bin:$PATH
+
+WORKDIR /workspace
+ENTRYPOINT ["/bin/bash"]