title: moduleNameMapper stopped working when upgrading to ts-jest 23
body: <p>I'm working on a project with a custom webpack build. React, Typescript, Jest tests in typescript as well.</p>
  
  <p>The tests have been working as expected for as long as I've been on the project. 
  Yesterday however I upgraded <code>ts-jest</code> to the latest version (24.x or 23.x) and some of my mappings stopped working, jest itself has been on 24 for a while.</p>
  
  <p>Anyone have a clue why this could happen? I've tried renaming the folder as it's in the <code>jest</code> folder and that seems odd to me (import from <code>jest/helpers/withProviders</code> confused me the first time is saw that). However it has been working fine for at least a year.</p>
  
  <p>Also I believe that when the target of the mapping is missing it should throw warnings or errors? It doesns't seem to do that when I change any of the mappings to something invalid. <strong>This did work on version 22!</strong></p>
  
  <h1>Edit:</h1>
  
  <p>If it was not clear, my error is on the line where I import our mock located in <code>/jest/helpers/withProviders</code> in my codebase (which works perfectly fine in ts-jest@22).</p>
  
  <p>here is my jest.config:</p>
  
  <pre><code>module.exports = {
    moduleNameMapper: {
      '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
        '&lt;rootDir&gt;/__mocks__/fileMock.js',
      '\\.(css|less|scss)$': 'identity-obj-proxy',
      '^jest[/](.+)': '&lt;rootDir&gt;/jest/$1',
      '^jest$': '&lt;rootDir&gt;/jest',
    },
    transform: {
      '^.+\\.tsx?$': 'ts-jest',
      '^.+project-name-framework.*\\.js$': './jest/transform.js',
    },
    transformIgnorePatterns: ['&lt;rootDir&gt;/node_modules/(?!@brand-name|@project-name)', '&lt;rootDir&gt;/src/utils/sso'],
    testRegex: '(/__tests__/.*|(\\.|/)(test|spec))\\.(jsx?|tsx?)$',
    testPathIgnorePatterns: ['&lt;rootDir&gt;/node_modules', '/__tests__/__mocks__/', '&lt;rootDir&gt;/cypress/'],
    moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
    testURL: 'http://localhost/some-brand-name',
    moduleDirectories: ['src', 'node_modules'],
    collectCoverage: false, // set this to true to show coverage reports
    collectCoverageFrom: [
      'src/components/**',
      'src/containers/**',
      'src/pages/**',
      'src/utils/**',
      '!**/__snapshots__/**',
      '!**/__mocks__/**',
    ],
    setupFilesAfterEnv: ['&lt;rootDir&gt;/jest/helpers/setup-tests.ts'],
  };
  </code></pre>