high

Jest: Failed to transform file

Jest's transformer (Babel, ts-jest, SWC) failed to process a file. The transformer may be misconfigured or the file contains unsupported syntax.

Common Causes

  1. 1Missing or incorrect transform config in jest.config
  2. 2Babel preset or plugin not installed
  3. 3TypeScript config errors
  4. 4File uses syntax not supported by the configured transformer version

How to Fix

Use @swc/jest for fast TypeScript transforms

// jest.config.ts
export default {
  transform: {
    '^.+\\.(t|j)sx?$': '@swc/jest',
  },
};

@swc/jest is significantly faster than ts-jest and handles most TypeScript and JSX features.

How ObserveOne Helps

ObserveOne validates test toolchain configurations and detects transform issues before they slow down CI.

Start Monitoring Free

Related Errors

Cannot find module './Component'

Jest could not resolve a module import. The file may not exist, the path may be wrong, or the module resolution config may be misconfigured.

SyntaxError: Unexpected token

Jest encountered syntax it cannot parse. This usually means a file needs to be transformed (e.g., TypeScript, JSX, ESM) but the transformer is not configured.

Snapshot mismatch — expected value to match snapshot

The rendered output does not match the stored snapshot. The component output changed since the snapshot was last updated.

Timeout — Async callback was not invoked within 5000ms

An async test did not complete within the default 5-second timeout. The async operation may be hanging, or done() was never called.

UnhandledPromiseRejectionWarning

A Promise was rejected but no .catch() handler or try/catch block caught the error. This can cause flaky tests or missed failures.