fix(require-hook): check variables are either const or declarations (#959)

Author: G-Rath

docs/rules/require-hook.md

@@ -19,7 +19,7 @@ directly within the body of a `describe`, _except_ for the following:
 
 - `import` statements
 - `const` variables
-- `let` _declarations_
+- `let` _declarations_, and initializations to `null` or `undefined`
 - Types
 - Calls to the standard Jest globals
 

src/rules/__tests__/require-hook.test.ts

@@ -76,6 +76,20 @@ ruleTester.run('require-hook', rule, {
         });
       });
     `,
+    dedent`
+      let consoleErrorSpy = null; 
+
+      beforeEach(() => {
+        consoleErrorSpy = jest.spyOn(console, 'error');
+      });
+    `,
+    dedent`
+      let consoleErrorSpy = undefined; 
+
+      beforeEach(() => {
+        consoleErrorSpy = jest.spyOn(console, 'error');
+      });
+    `,
     dedent`
       describe('some tests', () => {
         beforeEach(() => {
@@ -145,6 +159,27 @@ ruleTester.run('require-hook', rule, {
         },
       ],
     },
+    {
+      code: dedent`
+        let { setup } = require('./test-utils');
+
+        describe('some tests', () => {
+          setup();
+        });
+      `,
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 1,
+          column: 1,
+        },
+        {
+          messageId: 'useHook',
+          line: 4,
+          column: 3,
+        },
+      ],
+    },
     {
       code: dedent`
         describe('some tests', () => {
@@ -176,6 +211,73 @@ ruleTester.run('require-hook', rule, {
         },
       ],
     },
+    {
+      code: dedent`
+        let consoleErrorSpy = jest.spyOn(console, 'error');
+
+        describe('when loading cities from the api', () => {
+          let consoleWarnSpy = jest.spyOn(console, 'warn');
+        });
+      `,
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 1,
+          column: 1,
+        },
+        {
+          messageId: 'useHook',
+          line: 4,
+          column: 3,
+        },
+      ],
+    },
+    {
+      code: dedent`
+        let consoleErrorSpy = null;
+
+        describe('when loading cities from the api', () => {
+          let consoleWarnSpy = jest.spyOn(console, 'warn');
+        });
+      `,
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 4,
+          column: 3,
+        },
+      ],
+    },
+    {
+      code: 'let value = 1',
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 1,
+          column: 1,
+        },
+      ],
+    },
+    {
+      code: "let consoleErrorSpy, consoleWarnSpy = jest.spyOn(console, 'error');",
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 1,
+          column: 1,
+        },
+      ],
+    },
+    {
+      code: "let consoleErrorSpy = jest.spyOn(console, 'error'), consoleWarnSpy;",
+      errors: [
+        {
+          messageId: 'useHook',
+          line: 1,
+          column: 1,
+        },
+      ],
+    },
     {
       code: dedent`
         import { database, isCity } from '../database';
@@ -236,6 +338,11 @@ ruleTester.run('require-hook', rule, {
           line: 16,
           column: 1,
         },
+        {
+          messageId: 'useHook',
+          line: 31,
+          column: 3,
+        },
         {
           messageId: 'useHook',
           line: 33,

src/rules/require-hook.ts

@@ -8,6 +8,7 @@ import {
   isDescribeCall,
   isFunction,
   isHook,
+  isIdentifier,
   isTestCaseCall,
 } from './utils';
 
@@ -19,12 +20,28 @@ const isJestFnCall = (node: TSESTree.CallExpression): boolean => {
   return !!getNodeName(node)?.startsWith('jest.');
 };
 
+const isNullOrUndefined = (node: TSESTree.Expression): boolean => {
+  return (
+    (node.type === AST_NODE_TYPES.Literal && node.value === null) ||
+    isIdentifier(node, 'undefined')
+  );
+};
+
 const shouldBeInHook = (node: TSESTree.Node): boolean => {
   switch (node.type) {
     case AST_NODE_TYPES.ExpressionStatement:
       return shouldBeInHook(node.expression);
     case AST_NODE_TYPES.CallExpression:
       return !isJestFnCall(node);
+    case AST_NODE_TYPES.VariableDeclaration: {
+      if (node.kind === 'const') {
+        return false;
+      }
+
+      return node.declarations.some(
+        ({ init }) => init !== null && !isNullOrUndefined(init),
+      );
+    }
 
     default:
       return false;