ng test "Cannot resolve 'fs'" after updating to Angular 8

Question

After upgrading my Angular project to 8, I get this error when running ng-test --source-map false.

Note: I could not find an import of fs anywhere in my project code. AFAIK, my project has no special need to access the filesystem.

ERROR in ./node_modules/resolve/lib/async.js
Module not found: Error: Can't resolve 'fs' in 'C:\src\myproject\node_modules\resolve\lib'
resolve 'fs' in 'C:\src\myproject\node_modules\resolve\lib'
  Parsed request is a module
  using description file: C:\src\myproject\node_modules\resolve\package.json (relative path: ./lib)
    Field 'browser' doesn't contain a valid alias configuration
    resolve as module
      looking for modules in C:/src/myproject/src/
        using description file: C:\src\myproject\package.json (relative path: ./src/)
          Field 'browser' doesn't contain a valid alias configuration
          using description file: C:\src\myproject\package.json (relative path: ./src/fs)
            no extension
              Field 'browser' doesn't contain a valid alias configuration
              C:\src\myproject\src\fs doesn't exist
            .ts
              Field 'browser' doesn't contain a valid alias configuration
              C:\src\myproject\src\fs.ts doesn't exist

It looks like there is a library called resolve which requires fs. Here is what I found about resolve:

yarn why resolve
yarn why v1.16.0
[1/4] Why do we have the module "resolve"...?
[2/4] Initialising dependency graph...
[3/4] Finding dependency...
[4/4] Calculating file sizes...
=> Found "[email protected]"
info Has been hoisted to "resolve"
info Reasons this module exists
   - Hoisted from "tslint#resolve"
   - Hoisted from "grunt-cli#liftoff#resolve"
   - Hoisted from "@angular-devkit#build-angular#postcss-import#resolve"
   - Hoisted from "@angular-devkit#build-angular#@babel#core#resolve"
   - Hoisted from "grunt-cli#liftoff#rechoir#resolve"
   - Hoisted from "@angular#cli#pacote#normalize-package-data#resolve"
=> Found "grunt#[email protected]"
info Reasons this module exists
   - "grunt#grunt-cli" depends on it
   - Hoisted from "grunt#grunt-cli#resolve"
Done in 0.71s.

It seems normal that command-line tools like the angular CLI build and tslint should access the filesystem... so why is my project failing?

All of the above libs mentioned in yarn why (tslint, grunt-cli, angular-devkit, angular/cli) are listed under devDependencies, which seems OK to me.

Update

After working through a few other issues, I'm getting this error now on both ng serve and ng test. Here are my tsconfig files:

tsconfig.json:

{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "downlevelIteration": true,
    "experimentalDecorators": true,
    "module": "esnext",
    "moduleResolution": "node",
    "importHelpers": true,
    "target": "es2015",
    "typeRoots": [
      "node_modules/@types",
      "src/@types"
    ],
    "lib": [
      "es2018",
      "dom"
    ]
  },
  "angularCompilerOptions": {
    "fullTemplateTypeCheck": true,
    "strictInjectionParameters": true
  }
}

tsconfig.spec.json:

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "outDir": "./out-tsc/spec",
    "types": [
      "jasmine",
      "node"
    ]
  },
  "files": [
    "src/test.ts",
    "src/polyfills.ts"
  ],
  "include": [
    "src/**/*.spec.ts",
    "src/**/*.d.ts"
  ]
}

tsconfig.app.json:

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "outDir": "./out-tsc/app",
    "types": [
      "node"
    ]
  },
  "files": [
    "src/main.ts",
    "src/polyfills.ts"
  ],
  "include": [
    "src/**/*.ts"
  ],
  "exclude": [
    "src/test.ts",
    "**/*.spec.ts"
  ]
}

Answer 1

After a long trial-and-error elimination process, I found the culprit:

import {hasOwnProperty} from 'tslint/lib/utils';

I accidentally imported a tslint utility function into my application source code. Oops!