How to use docker-image-resource to build custom docker images used as inputs for later tasks

build-and-test.yml

jobs:
- name: build-and-test
  plan:
  - task: build-image
    privileged: true
    config:
      platform: linux
      image_resource:
        type: docker-image
        source:
          repository: concourse/docker-image-resource
      outputs:
      - name: image-output
      params:
        DESTINATION: image-output
        WORKSPACE: /tmp/scratch
      run:
        path: /bin/bash
        args:
        - -c
        - |
          set -eux
          
          ## Need this, but depends on internals of docker-image-resource
          ## maybe can be replaced with your own scripts to start_docker
          source /opt/resource/common.sh
          
          start_docker "[]" ""
          
          
          ## This should be done via inputs
          mkdir -p "${WORKSPACE}/git-master"
          
          cat << EOF > "${WORKSPACE}/git-master/package.json"
          {
            "name": "node-js-sample",
            "version": "0.2.0",
            "description": "A sample Node.js app using Express 4",
            "main": "index.js",
            "scripts": {
              "start": "node index.js"
            },
            "dependencies": {
              "express": "^4.13.3"
            },
            "engines": {
              "node": "4.0.0"
            },
            "repository": {
              "type": "git",
              "url": "https://github.com/heroku/node-js-sample"
            },
            "keywords": [
              "node",
              "heroku",
              "express"
            ],
            "author": "Mark Pundsack",
            "contributors": [
              "Zeke Sikelianos <zeke@sikelianos.com> (http://zeke.sikelianos.com)"
            ],
            "license": "MIT"
          }
          EOF
          
          cat << EOF > "${WORKSPACE}/Dockerfile"
          FROM node:8.1.2-alpine

          ADD git-master /tmp/git-master

          RUN (cd /tmp/git-master && npm install)
          RUN mv /tmp/git-master/node_modules .
          EOF
          
          
          ## The meat of what you are doing
          docker build -t test "${WORKSPACE}"
          
          docker run \
              --cidfile=/tmp/container.cid \
              -v /opt/resource/print-metadata:/tmp/print-metadata \
              --entrypoint /tmp/print-metadata  \
              test > "${DESTINATION}/metadata.json"
              
          mkdir -p "${DESTINATION}/rootfs/"
          
          docker export $(cat /tmp/container.cid) | tar --exclude="dev/*" -xf - -C "${DESTINATION}/rootfs/"
          
  - task: check-if-it-worked
    image: image-output
    config:
      platform: linux
      run: 
        path: echo
        args:
        - /tmp/git-master/package.json

Hmm, NPM doesn't seem to work in the exported image:

          docker run \
              --cidfile=/tmp/container.cid \
              -v /opt/resource/print-metadata:/tmp/print-metadata \
              --entrypoint /tmp/print-metadata  \
              test > "${DESTINATION}/metadata.json"
+
+         # Works when same image is run directly
+         docker run test echo "NPM Version is "
+         docker run test npm --version
              
          mkdir -p "${DESTINATION}/rootfs/"
          
          docker export $(cat /tmp/container.cid) | tar --exclude="dev/*" -xf - -C "${DESTINATION}/rootfs/"
          
  - task: check-if-it-worked
    image: image-output
    config:
      platform: linux
      run: 
+        # running with output of `docker export` fails, see screenshot below
-        path: echo
+        path: npm
        args:
-        - /tmp/git-master/package.json
+        - --version

Testing npm --version with the image directly:

Testing npm --version with the exported image: