Feat: add linting rule for before/beforeEach just like the async rule for test

Author: Arcturus5404

README.md

@@ -36,6 +36,7 @@ You can add rules:
     "cypress/assertion-before-screenshot": "warn",
     "cypress/no-force": "warn",
     "cypress/no-async-tests": "error",
+    "cypress/no-async-before": "error",
     "cypress/no-pause": "error"
   }
 }

docs/rules/no-async-before.md

@@ -0,0 +1,52 @@
+# Prevent using async/await in Cypress test cases (no-async-tests)
+
+Cypress before that return a promise will cause tests to prematurely start, can cause unexpected behavior. An `async` function returns a promise under the hood, so a before using an `async` function might also error.
+
+## Rule Details
+
+This rule disallows using `async` before and beforeEach functions.
+
+Examples of **incorrect** code for this rule:
+
+```js
+describe('my feature', () => {
+  before('my test case', async ()  => {
+    await cy.get('.myClass')
+    // other operations
+  })
+})
+```
+
+```js
+describe('my feature', () => {
+  before('my test case', async ()  => {
+    cy
+    .get('.myClass')
+    .click()
+
+    await someAsyncFunction()
+  })
+})
+```
+
+Examples of **correct** code for this rule:
+
+```js
+describe('my feature', () => {
+  before('my test case', ()  => {
+    cy.get('.myClass')
+    // other operations
+  })
+})
+
+```
+
+## When Not To Use It
+
+If there are genuine use-cases for using `async/await` in your before then you may not want to include this rule (or at least demote it to a warning).
+
+## Further Reading
+
+- [Commands Are Asynchronous](https://docs.cypress.io/guides/core-concepts/introduction-to-cypress.html#Commands-Are-Asynchronous)
+- [Commands Are Promises](https://docs.cypress.io/guides/core-concepts/introduction-to-cypress.html#Commands-Are-Promises)
+- [Commands Are Not Promises](https://docs.cypress.io/guides/core-concepts/introduction-to-cypress.html#Commands-Are-Not-Promises)

lib/rules/no-async-before.js

@@ -0,0 +1,47 @@
+'use strict'
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Prevent using async/await in Cypress before methods',
+      category: 'Possible Errors',
+      recommended: true,
+    },
+    messages: {
+      unexpected: 'Avoid using async functions with Cypress before / beforeEach functions',
+    },
+  },
+
+  create (context) {
+    function isBeforeBlock (callExpressionNode) {
+      const { type, name } = callExpressionNode.callee
+
+      return type === 'Identifier'
+                && name === 'before' || name === 'beforeEach'
+    }
+
+    function isBeforeAsync (node) {
+      return node.arguments
+                && node.arguments.length >= 2
+                && node.arguments[1].async === true
+    }
+
+    return {
+      Identifier (node) {
+        if (node.name === 'cy' || node.name === 'Cypress') {
+          const ancestors = context.getAncestors()
+          const asyncTestBlocks = ancestors
+          .filter((n) => n.type === 'CallExpression')
+          .filter(isBeforeBlock)
+          .filter(isBeforeAsync)
+
+          if (asyncTestBlocks.length >= 1) {
+            asyncTestBlocks.forEach((node) => {
+              context.report({ node, messageId: 'unexpected' })
+            })
+          }
+        }
+      },
+    }
+  },
+}

tests/lib/rules/no-async-before.js

@@ -0,0 +1,25 @@
+'use strict'
+
+const rule = require('../../../lib/rules/no-async-tests')
+const RuleTester = require('eslint').RuleTester
+
+const ruleTester = new RuleTester()
+
+const errors = [{ messageId: 'unexpected' }]
+// async functions are an ES2017 feature
+const parserOptions = { ecmaVersion: 8 }
+
+ruleTester.run('no-async-tests', rule, {
+  valid: [
+    { code: 'before(\'a before case\', () => { cy.get(\'.someClass\'); })', parserOptions },
+    { code: 'before(\'a before case\', async () => { await somethingAsync(); })', parserOptions },
+    { code: 'async function nonTestFn () { return await somethingAsync(); }', parserOptions },
+    { code: 'const nonTestArrowFn = async () => { await somethingAsync(); }', parserOptions },
+  ],
+  invalid: [
+    { code: 'before(\'a test case\', async () => { cy.get(\'.someClass\'); })', parserOptions, errors },
+    { code: 'beforeEach(\'a test case\', async () => { cy.get(\'.someClass\'); })', parserOptions, errors },
+    { code: 'before(\'a test case\', async function () { cy.get(\'.someClass\'); })', parserOptions, errors },
+    { code: 'beforeEach(\'a test case\', async function () { cy.get(\'.someClass\'); })', parserOptions, errors },
+  ],
+})