feat: add no-mocks-import rule (#246)

README.md

@@ -102,6 +102,7 @@ for more information about extending configuration files.
 | [no-identical-title][]       | Disallow identical titles                                         | ![recommended][] |                     |
 | [no-jasmine-globals][]       | Disallow Jasmine globals                                          | ![recommended][] | ![fixable-yellow][] |
 | [no-jest-import][]           | Disallow importing `jest`                                         | ![recommended][] |                     |
+| [no-mocks-import][]          | Disallow manually importing from `__mocks__`                      |                  |                     |
 | [no-large-snapshots][]       | Disallow large snapshots                                          |                  |                     |
 | [no-test-callback][]         | Using a callback in asynchronous tests                            |                  | ![fixable-green][]  |
 | [no-test-prefixes][]         | Disallow using `f` & `x` prefixes to define focused/skipped tests | ![recommended][] | ![fixable-green][]  |
@@ -138,6 +139,7 @@ for more information about extending configuration files.
 [no-identical-title]: docs/rules/no-identical-title.md
 [no-jasmine-globals]: docs/rules/no-jasmine-globals.md
 [no-jest-import]: docs/rules/no-jest-import.md
+[no-mocks-import]: docs/rules/no-mocks-import.md
 [no-large-snapshots]: docs/rules/no-large-snapshots.md
 [no-test-callback]: docs/rules/no-test-callback.md
 [no-test-prefixes]: docs/rules/no-test-prefixes.md

__tests__/rules.test.js

@@ -5,7 +5,7 @@ const path = require('path');
 const { rules } = require('../index');
 
 const ruleNames = Object.keys(rules);
-const numberOfRules = 30;
+const numberOfRules = 31;
 
 describe('rules', () => {
   it('should have a corresponding doc for each rule', () => {

docs/rules/no-mocks-import.md

@@ -0,0 +1,27 @@
+# Disallow manually importing from `__mocks__` (no-mocks-import)
+
+When using `jest.mock`, your tests (just like the code being tested) should
+import from `./x`, not `./__mocks__/x`. Not following this rule can lead to
+confusion, because you will have multiple instances of the mocked module:
+
+```js
+jest.mock('./x');
+const x1 = require('./x');
+const x2 = require('./__mocks__/x');
+
+test('x', () => {
+  expect(x1).toBe(x2); // fails! They are both instances of `./__mocks__/x`, but not referentially equal
+});
+```
+
+### Rule details
+
+This rule reports imports from a path containing a `__mocks__` component.
+
+Example violations:
+
+```js
+import thing from './__mocks__/index';
+require('./__mocks__/index');
+require('__mocks__');
+```

index.js

@@ -27,6 +27,7 @@ module.exports = {
         'jest/no-focused-tests': 'error',
         'jest/no-identical-title': 'error',
         'jest/no-jest-import': 'error',
+        // 'jest/no-mocks-import': 'error',
         'jest/no-jasmine-globals': 'warn',
         'jest/no-test-prefixes': 'error',
         'jest/valid-describe': 'error',

rules/__tests__/no-mocks-import.test.js

@@ -0,0 +1,96 @@
+'use strict';
+
+const rule = require('../no-mocks-import.js');
+const { RuleTester } = require('eslint');
+const ruleTester = new RuleTester();
+const message = `Mocks should not be manually imported from a __mocks__ directory. Instead use jest.mock and import from the original module path.`;
+
+ruleTester.run('no-mocks-import', rule, {
+  valid: [
+    {
+      code: 'import something from "something"',
+      parserOptions: { sourceType: 'module' },
+    },
+    'require("somethingElse")',
+    'require("./__mocks__.js")',
+    'require("./__mocks__x")',
+    'require("./__mocks__x/x")',
+    'require("./x__mocks__")',
+    'require("./x__mocks__/x")',
+    'require()',
+    'entirelyDifferent(fn)',
+  ],
+  invalid: [
+    {
+      code: 'require("./__mocks__")',
+      errors: [
+        {
+          endColumn: 22,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'require("./__mocks__/")',
+      errors: [
+        {
+          endColumn: 23,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'require("./__mocks__/index")',
+      errors: [
+        {
+          endColumn: 28,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'require("__mocks__")',
+      errors: [
+        {
+          endColumn: 20,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'require("__mocks__/")',
+      errors: [
+        {
+          endColumn: 21,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'require("__mocks__/index")',
+      errors: [
+        {
+          endColumn: 26,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'import thing from "./__mocks__/index"',
+      parserOptions: { sourceType: 'module' },
+      errors: [
+        {
+          endColumn: 38,
+          column: 1,
+          message,
+        },
+      ],
+    },
+  ],
+});

rules/no-mocks-import.js

@@ -0,0 +1,34 @@
+'use strict';
+
+const { posix } = require('path');
+const { getDocsUrl } = require('./util');
+
+const mocksDirName = '__mocks__';
+const message = `Mocks should not be manually imported from a ${mocksDirName} directory. Instead use jest.mock and import from the original module path.`;
+
+const isMockPath = path => path.split(posix.sep).includes(mocksDirName);
+
+module.exports = {
+  meta: {
+    docs: {
+      url: getDocsUrl(__filename),
+    },
+  },
+  create(context) {
+    return {
+      ImportDeclaration(node) {
+        if (isMockPath(node.source.value)) {
+          context.report({ node, message });
+        }
+      },
+      'CallExpression[callee.name="require"]'(node) {
+        if (node.arguments.length && isMockPath(node.arguments[0].value)) {
+          context.report({
+            loc: node.arguments[0].loc,
+            message,
+          });
+        }
+      },
+    };
+  },
+};