Instanbuljs coverage reporting for projects being tested by web-component-tester

Usage no npm install needed!

<script type="module">
  import advancedRestClientWctIstanbub from 'https://cdn.skypack.dev/@advanced-rest-client/wct-istanbub';


WCT-istanbub (fork for ARC & API components)

Istanbul coverage plugin for web-component-tester.

Use this plugin to collect and report test coverage (via istanbul) for your project on each test run.

In order to use this coverage plugin use at least version 6.4.0 of web-component-tester

Check out this test repository for an example with 'app' and travis build

This version has been adjusted to work with Polymer 3 components. As a difference to the original package it always adds **/node_modules/** to the ignored rules. Otherwise the test won't run at all.


npm install @advanced-rest-client/wct-istanbub --save-dev

Basic Usage

Add the following configuration to web-component-tester's config file.


module.exports = {
  plugins: {
    istanbub: {
      reporters: ["text-summary", "lcov"],
      include: [
      exclude: [


Below are the available configuration options:


An array of istanbul reporters to use.


Files to include in instrumentation, default the basepath will be added - /components/${packagename}/{includepaths}


Files to exclude from instrumentation (this trumps files 'included' with the option above).

By default the '/test/' is excluded as istanbub crashes on some of the test tooling used by most projects and testing the coverage of your test files is not really useful.

default the basepath will be added - /components/${packagename}/{excludepaths}


Path to an Istanbul configuration file.


Overrides for the default Istanbul configuration. Check the default configuration for all available options.


Don't add the basepath to the include & exclude array's for specific use-cases


Support for npm based on where to retrieve basic assets from node_modules instead of bower_components


Define support module import (node) or none, allowed values: node and none

Defaults to none if npm false or node if npm is true


Override the componentRequest check


Add babel plugins to default set: [importMeta, asyncGenerators, dynamicImport, objectRestSpread, optionalCatchBinding, flow, jsx], for example [dotallRegex]. Duplicates will be filtered out

Coverage Thresholds

In addition to measuring coverage, this plugin can be used to enforce coverage thresholds. If coverage does not meet the configured thresholds, then the test run will fail, even if all tests passed.

This requires specifying the thresholds option for the plugin

writeOnlyOnSuccess false

Set to true to write coverage only if all tests pass


The following configuration will cause the test run to fail if less than 100% of the statements in instrumented files are covered by tests.

module.exports = {
  plugins: {
    istanbub: {
      dir: "./coverage",
      reporters: ["text-summary", "lcov"],
      include: [
      exclude: [
      thresholds: {
        global: {
          statements: 100