Running into error - shelljs requirement

[eduwass]

When trying to create test cases this happened:

➜  dhg_tw git:(master) ✗ npm run create-test-cases

> create-test-cases
> create-test-cases

internal/modules/cjs/loader.js:905
  throw err;
  ^

Error: Cannot find module 'shelljs'
Require stack:
- /Users/eduwass/Sites/dhg/app/public/wp-content/themes/dhg_tw/node_modules/wp-theme-auditor/bin/create-test-cases.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:902:15)
    at Function.Module._load (internal/modules/cjs/loader.js:746:27)
    at Module.require (internal/modules/cjs/loader.js:974:19)
    at require (internal/modules/cjs/helpers.js:92:18)
    at Object.<anonymous> (/Users/eduwass/Sites/dhg/app/public/wp-content/themes/dhg_tw/node_modules/wp-theme-auditor/bin/create-test-cases.js:6:15)
    at Module._compile (internal/modules/cjs/loader.js:1085:14)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)
    at Module.load (internal/modules/cjs/loader.js:950:32)
    at Function.Module._load (internal/modules/cjs/loader.js:790:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [
    '/Users/eduwass/Sites/dhg/app/public/wp-content/themes/dhg_tw/node_modules/wp-theme-auditor/bin/create-test-cases.js'
  ]
}

Was resolved after adding shelljs to the theme root with:
npm install shelljs --save-dev

Is this expected?