Handle 'no-unused-expressions' violations due to use of Chai expect

[ianwalter]

Using a Chai expect expression in a test with the StandardJS ESLint config will throw the ESLint error:

error  Expected an assignment or function call and instead saw an expression  no-unused-expressions

Since Chai is bundled with Cypress I think it only makes sense that eslint-plugin-cypress handle this without the user having to install a separate plugin to handle Chai expressions.

[jennifer-shehane]

Can you give a short example of the test with expression you wrote that errored so we can test this?

[ianwalter]

Sure:

const onRequest = ({ request }) => {
  expect(request.body.email.billingUpdate).to.be.true
  expect(request.body.phone.documentUpdate).to.be.false
}

[Strajk]

👋Here's discussion about this topic eslint/eslint#2102

[jennifer-shehane]

Eslint decided to not address this issue as it is library specific. It seems that the best fix for this would be to add the eslint-plugin-chai-friendly plugin to our eslint config or some similar configuration to ignore chai's no-unused-expressions. @chrisbreiding thoughts?

[corysimmons]

@jennifer-shehane Just tested this out. Works great and still catches errors not related to Cypress/Chai. 👍

[chrisbreiding]

Because of the way ESLint plugins work, we can't bundle a plugin with our plugin and have it "just work". The user still needs to install the chai plugin manually as their own dependency. If we include the rule and a user doesn't install the plugin (which they might not even need if they're not using the no-unused-expressions rule), they'll get an error saying there's an unknown rule in their configuration.

So instead, I'm going to document this in the README.

[bmulholland]

Resurrecting an old issue, but there is now a way to bundle plugins together: https://www.npmjs.com/package/@rushstack/eslint-patch

As used by airbnb, for example: https://github.com/vuejs/eslint-config-airbnb/blob/main/packages/eslint-config-airbnb/CHANGELOG.md#700