jest test suite failed to run: unexpected token

TL;DR

Jest failed to parse a file, usually an untransformed ESM import or a non-JS asset. Find which file and token the error names, add the transform or moduleNameMapper entry, and re-run.

Error

Test suite failed to run
    Jest encountered an unexpected token
    /app/node_modules/some-lib/index.js:1
    ({"Object.[anonymous]":function(module,exports,require,__dirname,__filename,jest){import x from 'y';
                                                                                      ^^^^^^

Steps

1. Read the error: it names the file and the token (import, export, < for JSX/SVG). Expected: you know what failed to parse.
2. If it is ESM in nodemodules, add it to transformIgnorePatterns exceptions: `transformIgnorePatterns: ['nodemodules/(?!(some-lib)/)']`. Expected: Jest transforms that package.
3. If it is an asset (svg, css, image), map it: moduleNameMapper: { '[.](svg|css)$': '[rootDir]/test/__mocks__/fileMock.js' }. Expected: imports resolve to a stub.
4. If it is your own ESM source, ensure babel-jest or ts-jest is configured for it. Expected: your code transforms.
5. Re-run the single suite. Expected: the suite runs instead of failing to parse.

When to use

• Test suite failed to run with unexpected token.
• After adding a new dependency or asset import.

When not to use

• Tests run but fail (assertion or logic failures).
• TypeScript type errors (tsc, not Jest transform).

Tool compatibility

• Jest 27 through 30; babel-jest, ts-jest.

Variant phrasings

Jest encountered an unexpected token import

The ESM variant; fix with transformIgnorePatterns.

Jest unexpected token export

Same fix from the export side.

Why it happens

Jest transforms files with babel by default but skips node_modules. Any ESM or non-JS syntax outside the transform pipeline crashes the parser.

Edge cases

• transformIgnorePatterns is a denylist; the regex exception syntax is easy to get backwards.
• Dual CJS/ESM packages need the right main/module resolution; check the package's exports.
• Vitest handles ESM natively; migrating avoids this whole class of error.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_cNkoLABm3803XTlm07II2g