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Description

Saves the code coverage collected during Cypress tests

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Saves the code coverage collected during Cypress tests

Install

npm install -D @cypress/code-coverage

Note: this plugin assumes

cypress
is a peer dependency already installed in your project.

Add to your

cypress/support/index.js
file
import '@cypress/code-coverage/support'

Register tasks in your

cypress/plugins/index.js
file
module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)

// add other tasks to be registered here

// IMPORTANT to return the config object // with the any changed environment variables return config }

Instrument your application

This plugin DOES NOT instrument your code. You have to instrument it yourself using Istanbul.js tool. Luckily it is not difficult. For example, if you are already using Babel to transpile you can add babel-plugin-istanbul to your

.babelrc
and instrument on the fly.
{
  "plugins": ["istanbul"]
}

Please see the Examples section down below, you can probably find a linked project matching your situation to see how to instrument your application's source code before running end-to-end tests to get the code coverage.

If your application has been instrumented correctly, then you should see additional counters and instructions in the application's JavaScript resources, like the image down below shows.

Instrumented code

You should see the

window.__coverage__
object in the "Application under test iframe"

Window coverage object

If you have instrumented your application's code and see the

window.__coverage__
object, then this plugin will save the coverage into
.nyc_output
folder and will generate reports after the tests finish (even in the interactive mode). Find the LCOV and HTML report in the
coverage/lcov-report
folder.

Coverage report

That should be it! You should see messages from this plugin in the Cypress Command Log

Plugin messages

More information

App vs unit tests

You need to instrument your web application. This means that when the test does

cy.visit('localhost:3000')
any code the
index.html
requests should be instrumented by YOU. See Examples section for advice, usually you need to stick
babel-plugin-istanbul
into your pipeline somewhere.

If you are testing individual functions from your application code by importing them directly into Cypress spec files, this is called "unit tests" and Cypress can instrument this scenario for you. See Instrument unit tests section.

Reports

The

coverage
folder has results in several formats, and the coverage raw data is stored in
.nyc_output
folder. You can see the coverage numbers yourself. This plugin has
nyc
as a dependency, so it should be available right away. Here are common examples:
# see just the coverage summary
$ npx nyc report --reporter=text-summary
# see just the coverage file by file
$ npx nyc report --reporter=text
# save the HTML report again
$ npx nyc report --reporter=lcov

It is useful to enforce minimum coverage numbers. For example:

$ npx nyc report --check-coverage --lines 80
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |
 main.js  |     100 |      100 |     100 |     100 |
----------|---------|----------|---------|---------|-------------------

$ npx nyc report --check-coverage --lines 101 ----------|---------|----------|---------|---------|------------------- File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s ----------|---------|----------|---------|---------|------------------- All files | 100 | 100 | 100 | 100 | main.js | 100 | 100 | 100 | 100 | ----------|---------|----------|---------|---------|------------------- ERROR: Coverage for lines (100%) does not meet global threshold (101%)

Watch video How to read code coverage report to see how to read the HTML coverage report.

Instrument unit tests

If you test your application code directly from

specs
you might want to instrument them and combine unit test code coverage with any end-to-end code coverage (from iframe). You can easily instrument spec files using babel-plugin-istanbul for example.

Install the plugin

npm i -D babel-plugin-istanbul

Set your

.babelrc
file
{
  "plugins": ["istanbul"]
}

Put the following in

cypress/plugins/index.js
file to use
.babelrc
file
module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)
  on('file:preprocessor', require('@cypress/code-coverage/use-babelrc'))
  return config
}

Now the code coverage from spec files will be combined with end-to-end coverage.

Find example of a just the unit tests and JavaScript source files with collected code coverage in examples/unit-tests-js.

Alternative for unit tests

If you cannot use

.babelrc
for some reason (maybe it is used by other tools?), try using the Browserify transformer included with this module in
use-browserify-istanbul
file.
module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)
  on(
    'file:preprocessor',
    require('@cypress/code-coverage/use-browserify-istanbul')
  )
  return config
}

Instrument backend code

Example in examples/backend folder.

You can also instrument your server-side code and produce combined coverage report that covers both the backend and frontend code

  1. Run the server code with instrumentation. The simplest way is to use nyc. If normally you run
    node src/server
    then to run instrumented version you can do
    nyc --silent node src/server
    .
  2. Add an endpoint that returns collected coverage. If you are using Express, you can simply do
const express = require('express')
const app = express()
require('@cypress/code-coverage/middleware/express')(app)

Tip: you can register the endpoint only if there is global code coverage object, and you can exclude the middleware code from the coverage numbers

// https://github.com/gotwarlost/istanbul/blob/master/ignoring-code-for-coverage.md
/* istanbul ignore next */
if (global.__coverage__) {
  require('@cypress/code-coverage/middleware/express')(app)
}

If you use Hapi server, define the endpoint yourself and return the object

if (global.__coverage__) {
  require('@cypress/code-coverage/middleware/hapi')(server)
}

For any other server, define the endpoint yourself and return the coverage object:

if (global.__coverage__) {
  // add method "GET /__coverage__" and response with JSON
  onRequest = (response) => response.sendJSON({ coverage: global.__coverage__ })
}
  1. Save the API coverage endpoint in
    cypress.json
    file to let the plugin know where to call to receive the code coverage data from the server. Place it in
    env.codeCoverage
    object:
{
  "env": {
    "codeCoverage": {
      "url": "http://localhost:3000/__coverage__"
    }
  }
}

That should be enough - the code coverage from the server will be requested at the end of the test run and merged with the client-side code coverage, producing a combined report.

expectBackendCoverageOnly

If there is NO frontend code coverage, and you want to only collect the backend code coverage using Cypress tests, set

expectBackendCoverageOnly: true
in
cypress.json
file. Otherwise Cypress complains that it cannot find the frontend code coverage.

Default:

No frontend code coverage warning

After:

{
  "env": {
    "codeCoverage": {
      "url": "http://localhost:3003/__coverage__",
      "expectBackendCoverageOnly": true
    }
  }
}

Cypress knows to expect the backend code coverage only

Custom report folder

You can specify custom report folder by adding

nyc
object to the
package.json
file. For example to save reports to
cypress-coverage
folder, use:
{
  "nyc": {
    "report-dir": "cypress-coverage"
  }
}

Custom reporters

You can specify custom coverage reporter(s) to use. For example to output text summary and save JSON report in

cypress-coverage
folder set in your
package.json
folder:
{
  "nyc": {
    "report-dir": "cypress-coverage",
    "reporter": ["text", "json"]
  }
}

Tip: find list of reporters here

Custom NYC command

Sometimes NYC tool might be installed in a different folder not in the current or parent folder, or you might want to customize the report command. In that case, put the custom command into

package.json
in the current folder and this plugin will automatically use it.
{
  "scripts": {
    "coverage:report": "call NYC report ..."
  }
}

TypeScript users

TypeScript source files should be automatically included in the report, if they are instrumented.

See examples/ts-example, bahmutov/cra-ts-code-coverage-example or bahmutov/cypress-angular-coverage-example.

Include code

By default, the code coverage report includes only the instrumented files loaded by the application during the tests. If some modules are loaded dynamically, or are loaded by the pages NOT visited during any tests, these files are not going to be in the report - because the plugin does not know about them. You can include all expected source files in the report by using

include
list in the
package.json
file. The files without counters will have 0 percent code coverage.

For example, if you want to make sure the final report includes all JS files from the "src/pages" folder, set the "nyc" object in your

package.json
file.
{
  "nyc": {
    "all": true,
    "include": "src/pages/*.js"
  }
}

See example examples/all-files

Exclude code

You can exclude parts of the code or entire files from the code coverage report. See Istanbul guide. Common cases:

Exclude "else" branch

When running code only during Cypress tests, the "else" branch will never be hit. Thus we should exclude it from the branch coverage computation:

// expose "store" reference during tests
/* istanbul ignore else */
if (window.Cypress) {
  window.store = store
}

Exclude next logical statement

Often needed to skip a statement

/* istanbul ignore next */
if (global.__coverage__) {
  require('@cypress/code-coverage/middleware/express')(app)
}

Or a particular

switch
case
switch (foo) {
  case 1 /* some code */:
    break
  /* istanbul ignore next */
  case 2: // really difficult to hit from tests
    someCode()
}

Exclude files and folders

See

nyc
configuration and include and exclude options. You can include and exclude files using

minimatch
patterns in
.nycrc
file or using "nyc" object inside your
package.json
file.

For example, if you want to only include files in the

app
folder, but exclude
app/util.js
file, you can set in your
package.json
{
  "nyc": {
    "include": ["app/**/*.js"],
    "exclude": ["app/util.js"]
  }
}

Note: if you have

all: true
NYC option set, this plugin will check the produced
.nyc_output/out.json
before generating the final report. If the
out.json
file does not have information for some files that should be there according to
include
list, then an empty placeholder will be included, see PR 208.

Another important option is

excludeAfterRemap
. By default it is false, which might let excluded files through. If you are excluding the files, and the instrumenter does not respect the
nyc.exclude
setting, then add
excludeAfterRemap: true
to tell
nyc report
to exclude files. See examples/exclude-files.

Disable plugin

You can skip the client-side code coverage hooks by setting the environment variable

coverage
to
false
.
# tell Cypress to set environment variable "coverage" to false
cypress run --env coverage=false
# or pass the environment variable
CYPRESS_coverage=false cypress run

or set it to

false
in the
cypress.json
file
{
  "env": {
    "coverage": false
  }
}

See Cypress environment variables and support.js. You can try running without code coverage in this project yourself

# run with code coverage
npm run dev
# disable code coverage
npm run dev:no:coverage

Links

Examples

Internal examples

Full examples we use for testing in this repository:

External examples

Look up the list of examples under GitHub topic cypress-code-coverage-example

Migrations

v2 to v3

Change the plugins file

cypress/plugins/index.js
// BEFORE
module.exports = (on, config) => {
  on('task', require('@cypress/code-coverage/task'))
}
// AFTER
module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)
  // IMPORTANT to return the config object
  // with the any changed environment variables
  return config
}

Tip: we include plugins.js file you can point at from your code in simple cases. From your

cypress.json
file:
{
  "pluginsFile": "node_modules/@cypress/code-coverage/plugins",
  "supportFile": "node_modules/@cypress/code-coverage/support"
}

See examples/use-plugins-and-support

Debugging

This plugin uses debug module to output additional logging messages from its task.js file. This can help with debugging errors while saving code coverage or reporting. In order to see these messages, run Cypress from the terminal with environment variable

DEBUG=code-coverage
. Example using Unix syntax to set the variable:
$ DEBUG=code-coverage npm run dev
...
  code-coverage reset code coverage in interactive mode +0ms
  code-coverage wrote coverage file /code-coverage/.nyc_output/out.json +28ms
  code-coverage saving coverage report using command: "nyc report --report-dir ./coverage --reporter=lcov --reporter=clover --reporter=json" +3ms

Deeply nested object will sometimes have

[object Object]
values printed. You can print these nested objects by specifying a deeper depth by adding
DEBUG_DEPTH=
setting
$ DEBUG_DEPTH=10 DEBUG=code-coverage npm run dev

Common issues

Common issue: not instrumenting your application when running Cypress.

If the plugin worked before in version X, but stopped after upgrading to version Y, please try the released versions between X and Y to see where the breaking change was.

If you decide to open an issue in this repository, please fill all information the issue template asks. The issues most likely to be resolved have debug logs, screenshots and hopefully public repository links so we can try running the tests ourselves.

Contributing

You can test changes locally by running tests and confirming the code coverage has been calculated and saved.

npm run test:ci
# now check generated coverage numbers
npx nyc report --check-coverage true --lines 80
npx nyc report --check-coverage true --lines 100 --include cypress/about.js
npx nyc report --check-coverage true --lines 100 --include cypress/unit.js

Tip: use check-code-coverage for stricter code coverage checks than

nyc report --check-coverage
allows.

Markdown

You can validate links in Markdown files in this directory by executing (Linux + Mac only) script

npm run check:markdown

License

This project is licensed under the terms of the MIT license.

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