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Jest encountered an unexpected token
    This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript.
    By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules".
    Here's what you can do:
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.
    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/en/configuration.html
    Details:
    C:\Code\SPFx\BCO\node_modules\@microsoft\sp-core-library\lib\index.js:11
    export { default as _BrowserDetection } from './BrowserDetection';
    ^^^^^^
    SyntaxError: Unexpected token export
      19 | } from 'office-ui-fabric-react/lib/Utilities';
      20 | import { IUserProvider } from "../UserProviders/IUserProvider";
    > 21 | import {
      22 |   Environment,
      23 |   EnvironmentType
      24 | } from '@microsoft/sp-core-library';
      at ScriptTransformer._transformAndBuildScript (node_modules/jest/node_modules/jest-runtime/build/script_transformer.js:403:17)
      at Object.<anonymous> (src/webparts/BCO/components/EmployeeSelector/EmployeeSelector.tsx:21:1)
      at Object.<anonymous> (src/webparts/BCO/components/FieldMapping/FieldMapping.tsx:13:1)
And tried these transformIgnorePatterns expressions in config.json
"transformIgnorePatterns": [
  "\\node_modules\\@microsoft\\sp-dialog",
  "\\node_modules\\@microsoft\\sp-core-library",
  "node_modules/(?!sp-core-library)",
  "node_modules/(?!@microsoft/sp-core-library)"
and none of them worked. I run this on Windows 10 so I tried also this format
                Anyone have a clue how to resolve this issue?  In my case, I have components that extend Vuetify components (aka import { VDataTable } from 'vuetify/lib').  The JEST documentation is seriously lacking on this complex configuration.  More practical, common examples would be helpful.
– RashadRivera
                Oct 16, 2020 at 20:57
                Try "@microsoft[/\\]sp-dialog" or more likely "@microsoft[/\\\\]sp-dialog". I believe it needs to be double escaped here.
– Estus Flask
                Mar 4, 2021 at 7:11
The transformIgnorePatterns means if the test path matches any of the patterns, it will not be transformed.
Note: DO NOT SPLIT MULTI-LINES.
The jest will ignore all node_modules via default. 
So you must write like this:
"transformIgnorePatterns": [
  // all exceptions must be first line
  "/node_modules/(?!@microsoft/sp-core-library|sp-dialog|other_libs_need_transform)"
Actually, it seems like typescript is not going well with JEST test cases, so what i feel like either JEST need to ignore those files or those packages need to be transpiled to js code which JEST can understand,
you can try this
"transformIgnorePatterns": [ "node_modules/(?!(@microsoft/sp-core-library))" ],
and in tsconfig.json
"allowJs": true,
for more details please check this post
https://github.com/SharePoint/sp-dev-docs/issues/2325#issuecomment-446416878
                just want to highlight from this answer the "allowJs": true at tsconfig.json. In my case this was exactly what I was missing and no one was mentioning it. Thanks @Vinay !
– Manu Artero
                Aug 1, 2022 at 8:18
I had a similar error while working on a project with jest, webpack, and vanilla js, so that error is thrown when jest encounters this line of code import '../css/styles.css';  in any /*?.js$/ file.
I solved it by moving the jest configurations from the package.json file into a jest.config.js file with the following minimal configuration:
// jest.config.js
module.exports = 
  "moduleNameMapper": {
    "\\.(css|less|scss)$": "identity-obj-proxy"
Then in babel.config.js:
module.exports = {
  presets: [
      '@babel/preset-env',
        targets: {
          node: 'current',
        
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