@cypress/code-coverage #472

This is the bug repro for cypress-io/code-coverage#472.

Context

It is a minimal example with the following requirements:

• Is an ESM module
  • i.e. "type": "module" is explicitly marked in the package.json
  • appropriate Cypress files need to be marked as .cjs in order for the tests to run. In cypress/plugins/index.cjs and fields in cypress.json.
• Uses component testing (i.e. @cypress/react and using open-ct and run-ct test runners).
• Uses code coverage (i.e. @cypress/code-coverage and babel-plugin-istanbul based on the official docs for instrumentation).

The requirements above are needed in the actual bug faced in the project, so the repo is capturing the minimal configuration of reproducing the same bug.

Reproduce

npm i
npm test

The test runner runs fine, and tests the code correctly.

Expected Behavior

Code coverage to output something meaningful in .nyc_output/out.json

Actual Behavior

.nyc_output/out.json is an empty object. The test runner complains that the code is not instrumented.

Context

To give context on the actual project where I first encountered the bug:

• I'm building a component library (does not actually use React).
• The code is authored as an ESM module (hence the repro repo being explicit about it in package.json and also having to use .cjs for some Cypress related setup to get the test runner working).
• I'm using @cypress/react and the component test runner for its delightful testing experience. That has been superb, it's just the last stretch of figuring out coverage that I'm hitting a wall. As a result, while React is not a dependency of the library I'm writing, it is a dev dependency for my tests. I definitely do not use create-react-app, and therefore have a custom .webpack.config.cjs and .babelrc in the cypress/ folder.

I don't fully understand why code coverage is not working, but some suspicions I have if they are helpful for the debugger:

• Maybe it's related to my package being ESM-only? (i.e. "type": "module" required in package.json).
• Maybe @cypress/react does not interoperate well with @cypress/code-coverage with ESM (as mentioned in the earlier point)?
• Maybe it's related to peer dependency versions that I have installed (I simply installed the latest).
• Maybe I'm completely missing something despite spending days iterating on variations from the official docs (which has a very simple setup!).