coverage-putty

0.1.0 verified Fri May 01 auth: no javascript

coverage-putty is a transform preprocessor for Jest that uses Istanbul to exclude JavaScript helper functions generated by the TypeScript transpiler from coverage reports. Version 0.1.0 is the current release, with no recent updates. It helps avoid skewing coverage metrics with boilerplate TypeScript output. Only works with Jest and Istanbul; requires manual transform configuration. No competing packages address this exact niche.

Common errors

error Cannot find module 'coverage-putty' ↓

cause Package not installed or not listed in devDependencies.

fix

Run npm install coverage-putty --save-dev

error TypeError: Cannot read property 'transform' of undefined ↓

cause Jest configuration is missing or malformed.

fix

Ensure 'jest' key exists in package.json with 'transform' object containing the pattern.

Warnings

gotcha Transform file pattern must be a JavaScript RegExp string, not a file glob. ↓

fix Ensure the pattern starts with 'src/' and includes proper escaping for dots: 'src/.*\\.js$'.

gotcha coverage-putty only works with JavaScript files that are output of TypeScript compilation; will not work if you point it at .ts files. ↓

fix Compile TypeScript to JS first (e.g., via ts-jest or tsc), then apply the transform on the JS files.

deprecated The package has not been updated since 2018; may not be compatible with latest Jest versions. ↓

fix Consider using 'jest-coverage-ignore' or similar alternatives, or test with your Jest version.

Install

npm install coverage-putty

yarn add coverage-putty

pnpm add coverage-putty

Imports

istanbul-ignore.js

wrong

transform: { 'src/.*\\.js$': 'coverage-putty' }

correct

transform: { 'src/.*\\.js$': 'coverage-putty/istanbul-ignore.js' }

The transform expects a path to the file istanbul-ignore.js inside the package.

Coordination
wrong
```
npm install coverage-putty --save
```
correct
```
npm install coverage-putty --save-dev
```
This is a dev dependency, used only during testing.
Configuration
wrong
```
Use transformIgnorePatterns
```
correct
```
Use Jest's transform option in package.json or jest.config.js
```
transformIgnorePatterns is for ignoring modules from transforming, not for applying a custom transform.

Quickstart

Configures Jest to use coverage-putty for transforming JS files, excluding TypeScript-generated helpers from coverage.

// package.json
{
  "jest": {
    "collectCoverage": true,
    "coverageDirectory": "report/",
    "collectCoverageFrom": [ "src/**/*.js" ],
    "transform": {
      "src/.*\\.js$": "coverage-putty/istanbul-ignore.js"
    }
  }
}

// Run tests
npx jest --coverage