nyc

What is nyc?

The nyc npm package is a command-line tool that allows for JavaScript code coverage. It is built on top of Istanbul and works well with subprocesses. It is often used for tracking how well your unit-tests exercise your codebase.

What are nyc's main functionalities?

Code Coverage

This feature allows you to collect code coverage information from your tests. You can use it with a test runner like mocha by adding it to your npm scripts in your package.json file.

"scripts": {
  "test": "nyc mocha"
}

Check Coverage Thresholds

nyc can enforce coverage thresholds. If code coverage falls below the specified thresholds, nyc will exit with a failure status. This is useful for maintaining a high standard of test coverage in a project.

"scripts": {
  "test": "nyc --check-coverage --lines 95 --functions 95 --branches 95 mocha"
}

Report Generation

After running your tests with nyc, you can generate various types of coverage reports. This example shows how to generate a report in the 'lcov' format, which can be used with tools that support lcov coverage reports.

"scripts": {
  "coverage": "nyc report --reporter=text-lcov > coverage.lcov"
}

Integration with CI/CD

nyc can be integrated with continuous integration/continuous deployment (CI/CD) systems. In this example, coverage information is piped to the 'coveralls' service to track coverage over time.

"scripts": {
  "coveralls": "nyc report --reporter=text-lcov | coveralls"
}

Other packages similar to nyc

istanbul

Istanbul is the underlying tool that nyc is built upon. It provides a JavaScript code coverage tool that computes statement, line, function, and branch coverage with module loader hooks to instrument code on the fly.

c8

c8 is a code coverage tool that uses Node.js' built-in V8 coverage. It is similar to nyc but does not use instrumented code and is built directly on V8's native coverage features, potentially providing more accurate coverage metrics.

jest

Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works out of the box for any React project. Jest provides its own way to track code coverage without needing an additional package like nyc.

blanket

Blanket is a simple code coverage library for JavaScript that works both in the browser and with Node.js. It is less commonly used now and has been largely superseded by tools like nyc and istanbul.

README

nyc

a code coverage reporter built on istanbul that works well for applications that spawn child processes.