output coverage reports using Node.js' built in coverage
npm install c8
!nycrc config on GitHub
Code-coverage using Node.js' built in functionality
that's compatible with Istanbul's reporters.
Like nyc, c8 just magically works:
``sh`
npm i c8 -g
c8 node foo.js
The above example will output coverage metrics for foo.js.
c8 can be configured via command-line flags, a c8 section in package.json, or a JSON configuration file on disk.
A configuration file can be specified by passing its path on the command line with --config or -c. If no config option is provided, c8 searches for files named .c8rc, .c8rc.json, .nycrc, or .nycrc.json, starting fromcwd and walking up the filesystem tree.
When using package.json configuration or a dedicated configuration file, omit the -- prefix from the long-form of the desired command-line option.
Here is a list of common options. Run c8 --help for the full list and documentation.
| Option | Description | Type | Default |
| ------ | ----------- | ---- | ------- |
| -c, --config | path to JSON configuration file | string | See above |-r
| , --reporter | coverage reporter(s) to use | Array | ['text'] |-o
| , --reports-dir, --report-dir | directory where coverage reports will be output to | string | ./coverage |--all
| | see section below for more info | boolean | false |--src
| | see section below for more info | Array | [process.cwd()]|-n
| , --include | see section below for more info | Array | [] (include all files) |-x
| , --exclude | see section below for more info | Array | list |--exclude-after-remap
| | see section below for more info | boolean | false |-e
| , --extension | only files matching these extensions will show coverage | string \| Array | list |--skip-full
| | do not show files with 100% statement, branch, and function coverage | boolean | false |--check-coverage
| | check whether coverage is within thresholds provided | boolean | false |--per-file
| | check thresholds per file | boolean | false |--temp-directory
| | directory V8 coverage data is written to and read from | string | process.env.NODE_V8_COVERAGE |--clean
| | should temp files be deleted before script execution | boolean | true |--experimental-monocart
| | see section below for more info | boolean | false |
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 coverage100%
could show as for a.js when in fact both main.js and b.js are uncovered.
By supplying --all to c8, all files in directories specified with --src (defaults to cwd) that pass the --include
and 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 can handle source-maps, for remapping coverage from generated code to original source files (_useful for TypeScript, JSX, etc_).
Just-in-time instrumented codebases will often insert source maps inline with the .js code they generate at runtime (e.g, @babel/register can be configured to insert a source map footer).
Pre-instrumented codebases, e.g., running tsc to generate .js in a build folder, may generate either inline source maps, or a separate .map file stored on disk.
c8 can handle loading both types of source maps.
Depending on the size and configuration of your project, it may be preferable to apply exclusion logic either before or after source-maps are used to remap compiled to original source files.
--exclude-after-remap is used to control this behaviour.
run c8 report to regenerate reports after c8 has already been run.
c8 can fail tests if coverage falls below a threshold.
After running your tests with c8, simply run:
`sh`
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:
`sh`
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:
`sh`
c8 check-coverage --lines 95 --per-file
If you want to check for 100% coverage across all dimensions, use --100:
`sh`
c8 --100 npm test
Is equivalent to
`sh`
c8 --check-coverage --lines 100 --functions 100 --branches 100 --statements 100 npm test
The --100 flag can be set for the check-coverage as well:
`sh`
c8 check-coverage --100
Monocart also provides reporters based directly on v8's byte-offset-based output. Such as, console-details and v8. This removes a complex transformation step and may be less bug prone for some environments.
Example usage:
`sh`
c8 --experimental-monocart --reporter=v8 --reporter=console-details node foo.js
NOTE: Monocart requires additional monocart-coverage-reports to be installed:
`sh`
npm i monocart-coverage-reports@2 --save-dev
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 /.
`js`
const myVariable = 99
/ c8 ignore next /
if (process.platform === 'win32') console.info('hello world')
`js`
const myVariable = 99
/ c8 ignore next 3 /
if (process.platform === 'win32') {
console.info('hello world')
}
`js`
/ c8 ignore start /
function dontMindMe() {
// ...
}
/ c8 ignore stop /
`js`
const myVariable = 99
const os = process.platform === 'darwin' ? 'OSXy' / c8 ignore next / : 'Windowsy'
c8 uses native V8 coverage,
make sure you're running Node.js >= 12.
See the contributing guide here.