c8 - native V8 code-coverage

Code-coverage using Node.js' built in functionality that's compatible with Istanbul's reporters.

Like nyc, c8 just magically works:

npm i c8 -g
c8 node foo.js

The above example will output coverage metrics for foo.js.

Checking for "full" source coverage using --all

By default v8 will only give us coverage for files that were loaded by the engine. If there are source files in your project that are flexed in production but not in your tests, your coverage numbers will not reflect this. For example, if your project's main.js loads a.js and b.js but your unit tests only load a.js your total coverage could show as 100% for a.js when in fact both main.js and b.js are uncovered.

By supplying --all to c8, all files in cwd that pass the --include and --exclude flag checks, will be loaded into the report. If any of those files remain uncovered they will be factored into the report with a default of 0% coverage.

c8 report

run c8 report to regenerate reports after c8 has already been run.

Checking coverage

c8 can fail tests if coverage falls below a threshold. After running your tests with c8, simply run:

c8 check-coverage --lines 95 --functions 95 --branches 95

c8 also accepts a --check-coverage shorthand, which can be used to both run tests and check that coverage falls within the threshold provided:

c8 --check-coverage --lines 100 npm test

The above check fails if coverage falls below 100%.

To check thresholds on a per-file basis run:

c8 check-coverage --lines 95 --per-file

Ignoring Uncovered Lines, Functions, and Blocks

Sometimes you might find yourself wanting to ignore uncovered portions of your codebase. For example, perhaps you run your tests on Linux, but there's some logic that only executes on Windows.

To ignore lines, blocks, and functions, use the special comment:

/* c8 ignore next */.

Ignoring the next line

const myVariable = 99
/* c8 ignore next */
if (process.platform === 'win32') console.info('hello world')

Ignoring the next N lines

const myVariable = 99
/* c8 ignore next 3 */
if (process.platform === 'win32') {
  console.info('hello world')
}

Ignoring all lines until told

/* c8 ignore start */
function dontMindMe() {
  // ...
}
/* c8 ignore stop */

Ignoring a block on the current line

const myVariable = 99
const os = process.platform === 'darwin' ? 'OSXy' /* c8 ignore next */ : 'Windowsy'

Supported Node.js Versions

c8 uses native V8 coverage, make sure you're running Node.js >= 10.12.0.

Contributing to c8

See the contributing guide here.