Troubleshooting

During your development with ts-jest, you may encounter various issues. Use this guide to resolve them.

Please also check Jest troubleshooting guide if your issue is related to jest.

Running ts-jest on CI tools

PROBLEM

Cannot find module "" from ""

SOLUTION

• Check if rootDir is referenced correctly. If not add this on your existing jest configuration.

jest.config.ts

import type { Config } from 'jest'

const config: Config = {
  //...
  roots: ['<rootDir>'],
}

export default config

• Check if module directories are included on your jest configuration. If not add this on your existing jest configuration.

jest.config.ts

import type { Config } from 'jest'

const config: Config = {
  //...
  moduleDirectories: ['node_modules', '<module-directory>'],
  modulePaths: ['<path-of-module>'],
}

export default config

• Check if module name is properly mapped and can be referenced by jest. If not, you can define moduleNameMapper for your jest configuration.

jest.config.ts

import type { Config } from 'jest'

const config: Config = {
  //...
  moduleNameMapper: {
    '<import-path>': '<rootDir>/<real-physical-path>',
  },
}

export default config

• Check github folder names if its identical to you local folder names. Sometimes github never updates your folder names even if you rename it locally. If this happens rename your folders via github or use this command git mv <source> <destination> and commit changes.

Transform (node)-module explicitly

PROBLEM

SyntaxError: Cannot use import statement outside a module

SOLUTION

One of the node modules doesn't have the correct syntax for Jest's execution step. It needs to be transformed first.

The error message usually shows which module is affected:

    SyntaxError: Cannot use import statement outside a module
    > 22 | import Component from "../../node_modules/some-module/lib";
         | ^

If the offending files are .mjs files

Use when individual files have a .mjs extension. Add a dedicated transform rule — ts-jest will transpile all .mjs files in node_modules to CommonJS without needing to list packages individually:

jest.config.ts

import type { Config } from 'jest'
import { createDefaultPreset } from 'ts-jest'

const presetConfig = createDefaultPreset()

const config: Config = {
  ...presetConfig,
  transformIgnorePatterns: ['node_modules/(?!.*\\.mjs$)'],
  transform: {
    ...presetConfig.transform,
    '^.+/node_modules/.+\\.mjs$': ['ts-jest', {}],
  },
}

export default config

If the offending package uses "type": "module" in its package.json

Use when a package declares "type": "module", causing its .js files to be treated as ESM. Name each affected package explicitly in transformIgnorePatterns:

jest.config.ts

import type { Config } from 'jest'

const config: Config = {
  //...
  transformIgnorePatterns: ['node_modules/(?!(some-module|another-module))'],
}

export default config

some-module and another-module will be transformed.

For more information see here and here.

Tests gets stuck when importing a dependency

PROBLEM

Without cache, jest takes an extremely long time to process files and appears to be stuck.

SOLUTION

ts-jest internally uses TypeScript compiler API to transform ts/js file into js file. The recommendation is to only transform what is needed.

A possible cause for that issue is that you may have enabled ts-jest to process javascript files in addition to TypeScript files. This leads to the result that more files are loaded which can, in some cases, blow up the machine.

• In your tsconfig file, check if compilerOptions.allowJs is unset or set to false.

tsconfig.json

{
  "compilerOptions": {
    "allowJs": false
  }
}

• In your jest configuration, check if the transform property includes only .ts files for ts-jest. If not, change the regular expression to exclude js files. You can also enable isolatedModules: true in tsconfig for ts-jest to use transpilation mode (similarly to other transpilers like Babel/SWC/Esbuild) for tests.

module.exports = {
  ...
  'transform': {
-    '^.+\\.(t|j)s$': ['ts-jest', {}],
+    '^.+\\.ts$': 'ts-jest',
  },
};

For more information see here