Jest – Simple tests are slow

Another possibility is that ts-jest is slow. There was an issue about that, and it was not completely resolved.

There are various workarounds discussed. They consist of setting isolatedModules=true and also --maxWorkers=1. That is, in jest.config.js

'use strict';

module.exports = {
    preset: 'ts-jest',
    testEnvironment: 'node',
    globals: {
        'ts-jest': {
            isolatedModules: true
        }
    },
}

and run

yarn test --maxWorkers=1

Could be worth trying. Alternatively, it is possible to forgo ts-jest and use babel transpilation.