nyc
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Istanbul's state of the art command line interface, with support for:
Instrumenting your code
You can install nyc as a development dependency and add it to the test stanza
in your package.json.
npm i nyc --save-dev
{
"scripts": {
"test": "nyc mocha"
}
}
Alternatively, you can install nyc globally and use it to execute npm test
:
npm i nyc -g
nyc npm test
nyc accepts a wide variety of configuration arguments, run nyc --help
for
thorough documentation.
Configuration arguments should be provided prior to the program that nyc
is executing. As an example, the following command executes npm test
,
and indicates to nyc that it should output both an lcov
and a text-lcov
coverage report.
nyc --reporter=lcov --reporter=text-lcov npm test
Accurate stack traces using source-maps
When produce-source-map
is set to true, then the instrumented source files will
include inline source maps for the instrumenter transform. When combined with
source-map-support,
stack traces for instrumented code will reflect their original lines.
Support for custom require hooks (babel, typescript, etc.)
nyc supports custom require hooks like @babel/register
. nyc can load
the hooks for you, using the --require
flag.
Source maps are used to map coverage information back to the appropriate lines
of the pre-transpiled code. You'll have to configure your custom require hook
to inline the source-map in the transpiled code. For Babel that means setting
the sourceMaps
option to inline
.
Source-Map support for pre-instrumented codebases
If you opt to pre-instrument your source-code (rather than using a just-in-time
transpiler like @babel/register
) nyc supports both inline source-maps and
.map
files.
Important: If you are using nyc with a project that pre-instruments its code,
run nyc with the configuration option --exclude-after-remap
set to false
.
Otherwise nyc's reports will exclude any files that source-maps remap to folders
covered under exclude rules.
Use with babel-plugin-istanbul
for Babel Support
We recommend using babel-plugin-istanbul
if your project uses the babel tool chain:
- enable the
babel-plugin-istanbul
plugin:
{
"babel": {
"presets": ["@babel/preset-env"],
"env": {
"test": {
"plugins": ["istanbul"]
}
}
}
}
Note: With this configuration, the Istanbul instrumentation will only be active when NODE_ENV
or BABEL_ENV
is test
unless the environment is a valid entry in "env"
within the .babelrc
file.
We recommend using the cross-env
package to set these environment variables
in your package.json
scripts in a way that works cross-platform.
- disable nyc's instrumentation and source-maps, e.g. in
package.json
:
{
"nyc": {
"require": [
"@babel/register"
],
"sourceMap": false,
"instrument": false
},
"scripts": {
"test": "cross-env NODE_ENV=test nyc mocha"
}
}
That's all there is to it, better ES2015+ syntax highlighting awaits:
Support for alternate file extensions (.jsx, .mjs)
Supporting file extensions can be configured through either the configuration arguments or with the nyc
config section in package.json
.
nyc --extension .jsx --extension .mjs npm test
{
"nyc": {
"extension": [
".jsx",
".mjs"
]
}
}
Checking coverage
nyc can fail tests if coverage falls below a threshold.
After running your tests with nyc, simply run:
nyc check-coverage --lines 95 --functions 95 --branches 95
nyc also accepts a --check-coverage
shorthand, which can be used to
both run tests and check that coverage falls within the threshold provided:
nyc --check-coverage --lines 100 npm test
The above check fails if coverage falls below 100%.
To check thresholds on a per-file basis run:
nyc check-coverage --lines 95 --per-file
Running reports
Once you've run your tests with nyc, simply run:
nyc report
To view your coverage report:
You can use any reporters that are supported by istanbul
: clover
, cobertura
, html
, json-summary
, json
, lcov
, lcovonly
, none
, teamcity
, text-lcov
, text-summary
, text
.
nyc report --reporter=lcov
You can find examples of the output for various reporters here.
You also have the choice of using a custom reporter.
Install custom reporters as a development dependency and you can use the --reporter
flag to load and view them:
nyc report --reporter=<custom-reporter-name>
Setting the project root directory
nyc runs a lot of file system operations relative to the project root directory.
During startup nyc will look for the default project root directory.
The default project root directory is the first directory found that contains a package.json
file when searching from the current working directory up.
If nyc fails to find a directory containing a package.json
file, it will use the current working directory as the default project root directory.
You can change the project root directory with the --cwd
option.
nyc uses the project root directory when:
- looking for source files to instrument
- creating globs for include and exclude rules during file selection
- loading custom require hooks from the
require
array
nyc may create artefact directories within the project root, such as:
- the report directory,
<project-root>/coverage
- the cache directory,
<project-root>/node_modules/.cache/nyc
- the temp directory,
<project-root>/.nyc_output
Selecting files for coverage
By default, nyc only collects coverage for source files that are visited during a test.
It does this by watching for files that are require()
'd during the test.
When a file is require()
'd, nyc creates and returns an instrumented version of the source, rather than the original.
Only source files that are visited during a test will appear in the coverage report and contribute to coverage statistics.
nyc will instrument all files if the --all
flag is set or if running nyc instrument
.
In this case all files will appear in the coverage report and contribute to coverage statistics.
nyc will only collect coverage for files that are located under cwd
, and then only *.js
files or files with extensions listed in the extension
array.
You can reduce the set of instrumented files by adding include
and exclude
filter arrays to your config.
These allow you to shape the set of instrumented files by specifying glob patterns that can filter files from the default instrumented set.
The exclude
array may also use exclude negated glob patterns, these are specified with a !
prefix, and can restore sub-paths of excluded paths.
Globs are matched using minimatch.
We use the following process to remove files from consideration:
- Limit the set of instrumented files to those files in paths listed in the
include
array. - Remove any files that are found in the
exclude
array. - Restore any exclude negated files that have been excluded in step 2.
Using include and exclude arrays
If there are paths specified in the include
array, then the set of instrumented files will be limited to eligible files found in those paths.
If the include
array is left undefined all eligible files will be included, equivalent to setting include: ['**']
.
Multiple include
globs can be specified on the command line, each must follow a --include
, -n
switch.
If there are paths specified in the exclude
array, then the set of instrumented files will not feature eligible files found in those paths.
You can also specify negated paths in the exclude
array, by prefixing them with a !
.
Negated paths can restore paths that have been already been excluded in the exclude
array.
Multiple exclude
globs can be specified on the command line, each must follow a --exclude
, -x
switch.
The exclude
option has the following defaults settings:
[
'coverage/**',
'packages/*/test/**',
'test/**',
'test{,-*}.js',
'**/*{.,-}test.js',
'**/__tests__/**',
'**/node_modules/**',
'**/babel.config.js'
]
These settings exclude test
and __tests__
directories as well as test.js
, *.test.js
, and test-*.js
files.
Specifying your own exclude property completely replaces these defaults.
For example, the following config will collect coverage for every file in the src
directory regardless of whether it is require()
'd in a test.
It will also exclude any files with the extension .spec.js
.
{
"nyc": {
"all": true,
"include": [
"src/**/*.js"
],
"exclude": [
"**/*.spec.js"
]
}
}
Note: Be wary of automatic OS glob expansion when specifying include/exclude globs with the CLI.
To prevent this, wrap each glob in single quotes.
Including files within node_modules
We always add **/node_modules/**
to the exclude list, even if not specified in the config.
You can override this by setting --exclude-node-modules=false
.
For example, in the following config, "excludeNodeModules: false"
will prevent node_modules
from being added to the exclude rules.
The set of include rules then restrict nyc to only consider instrumenting files found under the lib/
and node_modules/@my-org/
directories.
The exclude rules then prevent nyc instrumenting anything in a test
folder and the file node_modules/@my-org/something/unwanted.js
.
{
"nyc": {
"all": true,
"include": [
"lib/**",
"node_modules/@my-org/**"
],
"exclude": [
"node_modules/@my-org/something/unwanted.js",
"**/test/**"
],
"excludeNodeModules": false
}
}
Require additional modules
The --require
flag can be provided to nyc
to indicate that additional
modules should be required in the subprocess collecting coverage:
nyc --require @babel/register --require @babel/polyfill mocha
Caching
nyc
's default behavior is to cache instrumented files to disk to prevent instrumenting source files multiple times, and speed nyc
execution times. You can disable this behavior by running nyc
with the --cache false
flag. You can also change the default cache directory from ./node_modules/.cache/nyc
by setting the --cache-dir
flag.
Configuring nyc
Any configuration options that can be set via the command line can also be specified in the nyc
stanza of your package.json, or within a seperate configuration file - a variety of flavors are available:
File name | File Association |
---|
.nycrc | JSON |
.nycrc.json | JSON |
.nycrc.yaml | YAML |
.nycrc.yml | YAML |
nyc.config.js | CommonJS export |
package.json:
{
"description": "These are just examples for demonstration, nothing prescriptive",
"nyc": {
"check-coverage": true,
"per-file": true,
"lines": 99,
"statements": 99,
"functions": 99,
"branches": 99,
"include": [
"src/**/*.js"
],
"exclude": [
"src/**/*.spec.js"
],
"ignore-class-method": "methodToIgnore",
"reporter": [
"lcov",
"text-summary"
],
"require": [
"./test/helpers/some-helper.js"
],
"extension": [
".jsx"
],
"cache": true,
"all": true,
"temp-dir": "./alternative-tmp",
"report-dir": "./alternative"
}
}
Configuration can also be provided by nyc.config.js
if programmed logic is required:
'use strict';
const {defaultExclude} = require('test-exclude');
const isWindows = require('is-windows');
let platformExclude = [
isWindows() ? 'lib/posix.js' : 'lib/win32.js'
];
module.exports = {
exclude: platformExclude.concat(defaultExclude)
};
Publish, and reuse, your nyc configuration
nyc allows you to inherit other configurations using the key extends
. As an example,
an alternative way to configure nyc for babel-plugin-istanbul
would be to use the
@istanbuljs/nyc-config-babel preset:
{
"nyc": {
"extends": "@istanbuljs/nyc-config-babel"
}
}
To publish and resuse your own nyc
configuration, simply create an npm module that
exports an index.json
with your nyc
config.
High and low watermarks
Several of the coverage reporters supported by nyc display special information
for high and low watermarks:
- high-watermarks represent healthy test coverage (in many reports
this is represented with green highlighting).
- low-watermarks represent sub-optimal coverage levels (in many reports
this is represented with red highlighting).
You can specify custom high and low watermarks in nyc's configuration:
{
"nyc": {
"watermarks": {
"lines": [80, 95],
"functions": [80, 95],
"branches": [80, 95],
"statements": [80, 95]
}
}
}
Parsing Hints (Ignoring Lines)
There may be some sections of your codebase that you wish to purposefully
exclude from coverage tracking, to do so you can use the following parsing
hints:
/* istanbul ignore if */
: ignore the next if statement./* istanbul ignore else */
: ignore the else portion of an if statement./* istanbul ignore next */
: ignore the next thing in the source-code (
functions, if statements, classes, you name it)./* istanbul ignore file */
: ignore an entire source-file (this should be
placed at the top of the file).
Ignoring Methods
There may be some methods that you want to universally ignore out of your classes
rather than having to ignore every instance of that method:
{
"nyc": {
"ignore-class-method": "render"
}
}
Integrating with TAP formatters
Many testing frameworks (Mocha, Tape, Tap, etc.) can produce TAP output. tap-nyc is a TAP formatter designed to look nice with nyc.
More tutorials
You can find more tutorials at http://istanbul.js.org/docs/tutorials
Other advanced features
Take a look at http://istanbul.js.org/docs/advanced/ and please feel free to contribute documentation.