feat: adds no jest import rule (#95)

docs/rules/no-jest-import.md

@@ -0,0 +1,20 @@
+# Disallow importing Jest(no-jest-import)
+
+The `jest` object is automatically in scope within every test file. The methods
+in the `jest` object help create mocks and let you control Jest's overall
+behavior. It is therefore completely unnecessary to import in `jest`, as Jest
+doesn't export anything in the first place.
+
+### Rule details
+
+This rule reports on any importing of Jest.
+
+To name a few: `var jest = require('jest');` `const jest = require('jest');`
+`import jest from 'jest';` `import {jest as test} from 'jest';`
+
+There is no correct usage of this code, other than to not import `jest` in the
+first place.
+
+## Further Reading
+
+\*[The Jest Object](https://facebook.github.io/jest/docs/en/jest-object.html)

index.js

@@ -6,6 +6,7 @@ const noDisabledTests = require('./rules/no-disabled-tests');
 const noFocusedTests = require('./rules/no-focused-tests');
 const noHooks = require('./rules/no-hooks');
 const noIdenticalTitle = require('./rules/no-identical-title');
+const noJestImport = require('./rules/no-jest-import');
 const noLargeSnapshots = require('./rules/no-large-snapshots');
 const noTestPrefixes = require('./rules/no-test-prefixes');
 const preferToBeNull = require('./rules/prefer-to-be-null');
@@ -67,6 +68,7 @@ module.exports = {
     'no-focused-tests': noFocusedTests,
     'no-hooks': noHooks,
     'no-identical-title': noIdenticalTitle,
+    'no-jest-import': noJestImport,
     'no-large-snapshots': noLargeSnapshots,
     'no-test-prefixes': noTestPrefixes,
     'prefer-to-be-null': preferToBeNull,

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

@@ -0,0 +1,72 @@
+'use strict';
+
+const rule = require('../no-jest-import.js');
+const RuleTester = require('eslint').RuleTester;
+const ruleTester = new RuleTester();
+const message = `Jest is automatically in scope. Do not import "jest", as Jest doesn't export anything.`;
+
+ruleTester.run('no-jest-import', rule, {
+  valid: [
+    {
+      code: 'import something from "something"',
+      parserOptions: { sourceType: 'module' },
+    },
+    'require("somethingElse")',
+    'entirelyDifferent(fn)',
+  ],
+  invalid: [
+    {
+      code: 'require("jest")',
+      errors: [
+        {
+          endColumn: 15,
+          column: 9,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'import jest from "jest"',
+      parserOptions: { sourceType: 'module' },
+      errors: [
+        {
+          endColumn: 24,
+          column: 1,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'var jest = require("jest")',
+      errors: [
+        {
+          endColumn: 26,
+          column: 20,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'import {jest as test} from "jest"',
+      parserOptions: { sourceType: 'module' },
+      errors: [
+        {
+          endColumn: 34,
+          column: 1,
+          message,
+        },
+      ],
+    },
+    {
+      code: 'const jest = require("jest")',
+      parserOptions: { sourceType: 'module' },
+      errors: [
+        {
+          endColumn: 28,
+          column: 22,
+          message,
+        },
+      ],
+    },
+  ],
+});

rules/no-jest-import.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const getDocsUrl = require('./util').getDocsUrl;
+const getNodeName = require('./util').getNodeName;
+const message = `Jest is automatically in scope. Do not import "jest", as Jest doesn't export anything.`;
+
+module.exports = {
+  meta: {
+    docs: {
+      url: getDocsUrl(__filename),
+    },
+  },
+  create(context) {
+    return {
+      ImportDeclaration(node) {
+        if (node.source.value === 'jest') {
+          context.report({
+            node,
+            message,
+          });
+        }
+      },
+      CallExpression(node) {
+        const calleeName = getNodeName(node.callee);
+        if (calleeName === 'require' && node.arguments[0].value === 'jest') {
+          context.report({
+            loc: {
+              end: {
+                column: node.arguments[0].loc.end.column,
+                line: node.arguments[0].loc.end.line,
+              },
+              start: node.arguments[0].loc.start,
+            },
+            message,
+          });
+        }
+      },
+    };
+  },
+};