unit testing in library created with create-react-native-library (ESM?) failures

[dcorbin]

I created a library using create-react-native-library. I then attempted to unit-test a react-native component. This includes introducing @testing-library/react-native.

When I run the tests, I get:

SyntaxError: /Users/dcorbin/projects/awesome-library/node_modules/react-native/Libraries/vendor/emitter/EventEmitter.js: Unexpected token, expected "]" (39:5)

  37 |
  38 | type Registry<TEventToArgsMap: {...}> = {
> 39 |   [K in keyof TEventToArgsMap]: Set<Registration<TEventToArgsMap[K]>>,
     |      ^
  40 | };
  41 |
  42 | /**

Here's the test

import { render } from '@testing-library/react-native';
import { Stupid } from '../stupid';
describe('simple rendering test', () => {
  test('test stupid component', () => {
    const screen = render(<Stupid name="Fred" />);
    expect(screen.getByTestId('stupid-view')).toHaveTextContent('Hello, Fred');
  });
});
`

and here's the stupid component:

import { View, Text } from 'react-native';

export function Stupid(props: { name: string }) {
return (
<View testID={'stupid-view'}>
<Text testID={'stupid-text'}>Hello {props.name}

);
}

Before I create this simple example, I was getting an syntax Error on an import deep in a react-native class.  

It's pretty clear to me that this problem is related to ESM vs CommonJS, and I read the doc page about and I read the FAQ, but could not figure out how to get my tests to run correctly.  In the example provided, it's a default javascript-only library with no other changes.  What am I doing wrong?

[satya164]

Try updating your babel config at the root to https://github.com/callstack/react-native-builder-bob/blob/main/packages/create-react-native-library/templates/common/babel.config.js#L1

[dcorbin]

Worked great. Thanks.

[dcorbin]

Looks like I spoke too soon. That fixed the sample project, but real project continues to have problems with import:

  ● Test suite failed to run

    Jest encountered an unexpected token

    Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.

    Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.

    By default "node_modules" folder is ignored by transformers.

    Here's what you can do:
     • If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to enable it.
     • If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript
     • 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/configuration
    For information about custom transformations, see:
    https://jestjs.io/docs/code-transformation

    Details:

   [redacted]/node_modules/@expo/vector-icons/build/AntDesign.js:2
    import createIconSet from './createIconSet';
    ^^^^^^

    SyntaxError: Cannot use import statement outside a module

      1 | import { type ColorValue, Text, View } from 'react-native';
      2 | import React, { type PropsWithChildren, useCallback } from 'react';
    > 3 | import { Ionicons } from '@expo/vector-icons';
        | ^
      4 |
      5 | export type DigitPlace = number;
      6 |

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1505:14)
      at Object.<anonymous> (node_modules/@expo/vector-icons/src/Icons.ts:3:1)
      at Object.require (src/DragLines.tsx:3:1)
      at Object.require (src/__tests__/DigitDragLine.test.tsx:2:1)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.681 s
Ran all test suites.

Back to the head-bashing.

[satya164]

For that you need to update your transformIgnorePatterns to include any libraries that need compilation, e.g. @expo/vector-icons

See: https://jestjs.io/docs/configuration#transformignorepatterns-arraystring