[BUG] results of npmInstall is not reachable from generator testsuite

[duncdrum]

Describe the bug
i would have expected the unit test to run inside the completely generated app but that isn't the case, which is great for performance, but puts the actual number of declared dependencies in package.json out of reach of the testsuite.

Expected behavior
The fully modified package.json to be present when the tests are running.

To Reproduce
add this to any of the generated app specs.

const assert = require('yeoman-assert')
const helpers = require('yeoman-test')
const fs = require('fs-extra')

// this is a dummy test 
  describe('npm Install succeeds', function () {
    it('package json has 8 dev deps', function (done) {
      assert.fileContent('package.json', 'supertest')
      done()
    })

result

AssertionError [ERR_ASSERTION]: package.json did not match 'supertest'. Contained:

{
  "name": "foo",
  "version": "1.0.0",
  "description": "My amazing foo application",
  "homepage": "",
  "bugs": "",
  "engines": {
    "node": ">=14.0.0"
  },
  "keywords": [
    "exist",
    "exist-db",
    "xml",
    "xql",
    "xquery"
  ],
  "author": {
    "name": "tester",
    "email": "te@st.er"
  },
  "license": "MIT",
  "scripts": {
    "test": "mocha test/mocha/ --recursive --exit && mocha test/xqs/*.js",
    "cypress": "cypress run"
  },
  "repository": ""
}