gatsby-cypress-with-code-coverage

Gatsby example site with Cypress E2E tests and code coverage

This repository was scaffolded from the official starter example. Then I have added babel-plugin-istanbul following the Gatsby Babel documentation

npm i -D babel-preset-gatsby babel-plugin-istanbul
+ babel-preset-gatsby@0.8.0
+ babel-plugin-istanbul@6.0.0

The .babelrc imports the plugins

{
  "plugins": [
    [
      "babel-plugin-istanbul"
    ]
  ],
  "presets": [
    [
      "babel-preset-gatsby",
      {
        "targets": {
          "browsers": [
            ">0.25%",
            "not dead"
          ]
        }
      }
    ]
  ]
}

Immediately you can see the window.__coverage__ object in the DevTools console

We do not want .cache files in the coverage list, we only want our local src files instrumented. We can modify the plugin's settings in .babelrc to include only files in the src folder.

{
  "plugins": [
    [
      "babel-plugin-istanbul", {
        "include": ["src/**/*.js"]
      }
    ]
  ]
}

The window.__coverage__ object now has a single entry.

We do not want to instrument the source code in production. Thus let's move the Istanbul plugin into develop environment

{
  "env": {
    "develop": {
      "plugins": [
        [
          "babel-plugin-istanbul",
          {
            "include": [
              "src/**/*.js"
            ]
          }
        ]
      ]
    }
  }
}

If you run npm run develop, the window.__coverage__ object will not be defined. If you execute NODE_ENV=develop npm run develop the code will be instrumented.

Let's add Cypress and its code coverage plugin

$ npm i -D cypress @cypress/code-coverage
+ cypress@6.0.1
+ @cypress/code-coverage@3.8.5

We can quickly scaffold a spec file to simply load the page and assert the "Hello" is there.

$ npx @bahmutov/cly init

Let's use start-server-and-test to start Gatsby and open Cypress

$ npm i -D start-server-and-test
+ start-server-and-test@1.11.6

In package.json define the scripts

{
  "scripts": {
    "develop": "gatsby develop",
    "cy:open": "cypress open",
    "dev": "NODE_ENV=develop start-test develop 8000 cy:open"
  }
}

Follow the instructions in the code coverage plugin to add it to the plugins and support files. Then use the command npm run dev to open Cypress. Run the test

// cypress/integration/spec.js
it("shows the Hello page", () => {
  cy.visit("/").contains("Hello world!")
})

Notice the code coverage log messages

Open the coverage HTML report (there are reports in different formats sorted in the folder `coverage)

$ open coverage/lcov-report/index.html

Inspect the report