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code-coverage-for-cypress.md

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description
Learn how to setup Cypress to start reporting code coverage results

Code Coverage for Cypress

Code Coverage for Cypress

{% hint style="info" %} TL;DR

See a working example GitHub repository

  • Install cypress-cloud version 1.9.5+
  • Install and configure Cypress Code coverage plugin as described here
  • Run cypress-cloud with --experimental-coverage-recording CLI flag enabled {% endhint %}

Enabling code coverage for Cypress involves the following steps:

  • Instrumenting the code and generating the coverage report (done by cypress runner together with Istanbul or any other coverage tool)
  • Uploading the report to Currents for processing (done by cypress-cloud package)

Instrumenting the code

Instrumenting the code and generating reports is well described in the detailed guide.

In short:

  • Install and configure the official @cypress/code-coverage plugin together with the @cypress/code-coverage/support support file (the plugin is developed and maintained by the Cypress.io team)
  • Add code instrumentation - for example, by using @cypress/code-coverage/use-babelrc for on-the-fly instrumentation

Uploading the reports to Currents

  • If you haven’t yet, install cypress-cloud; make sure to add cypress-cloud/plugin after @cypress/code-coverage
  • Optional: provide custom location for generated reports:
    • cypress-cloud expects to find the coverage reports at their default location at <projectRoot>/.nyc_output/out.json
    • You can provide a custom location by setting env.coverageFile in cypress.config.{jt}s

Example cypress.config.ts file

// cypress.config.ts
import coveragePlugin from "@cypress/code-coverage/task";
import coverageInstrumenter from "@cypress/code-coverage/use-babelrc";

import { cloudPlugin } from "cypress-cloud/plugin";

import { defineConfig } from "cypress";

export default defineConfig({
  e2e: {
    async setupNodeEvents(on, config) {
      // enable on-the-file instrumentation
      on("file:preprocessor", coverageInstrumenter);
      // enable coverage plugin to generate a report
      const tempConfig = coveragePlugin(on, config);
      // enable cypress-cloud plugin
      return await cloudPlugin(on, tempConfig);
    },
    baseUrl: "<http://localhost:8888>",
    supportFile: "cypress/support/e2e.js",
    specPattern: "cypress/**/*.cy.js",
    env: {
      // @cypress/code-coverage config
      // exclude test files from the reports
      codeCoverage: {
        exclude: ["cypress/**/*.*"],
      },
      // ⭐️ instruct cypress-cloud on the location of the generated report
      coverageFile: "./.nyc_output/out.json",
    },
  },
});

Example Cypress support.ts file

import "@cypress/code-coverage/support";
import "cypress-cloud/support";

Run cypress-cloud with coverage enabled

Running cypress-cloud with --experimental-coverage-recording flag will activate the collection of the coverage reports and send them to Currents for processing.

The script will discover the reports at the configured location ./.nyc_output/out.json by default, or an explicit location defined in env.coverageFile of cypress.config.{jt}s

Example:

{% code overflow="wrap" %}

npx cypress-cloud run --parallel --record --key <record_key> --ci-build-id <ci-build-id>  --experimental-coverage-recording

{% endcode %}