I’m trying to use Jest in my Express API with TypeScript. However, every time I try to execute npm run test, Jest complains about the ESM.

I’ve tried many configurations, but none of then solved the problem. Anyone knows how can I solve it?

I installed jest and ts-jest. My tests are in src/__tests__/. Here is my jest.config.js (created using npx ts-jest config:init):

/** @type {import('ts-jest').JestConfigWithTsJest} **/
export default {
    testEnvironment: 'node',
    transform: {
        '^.+\.(ts|tsx)$': ['ts-jest', {useESM: true}],
    },
    testMatch: ['**/**/*.test.ts'],
};

When I try to execute Jest, it throws:

Import assertions are only supported when the '--module' option is set to 'esnext', 'nodenext', or 'preserve'.

It happens because there is an assertion like this in app.ts, a file that is imported in a test:

import swaggerFile from '../swagger-output.json' assert { type: 'json' };