Remove ESLint extends and add Jest rules (facebook#9587)

packages/cra-template/template.json

@@ -18,6 +18,9 @@
       "react-toastify": "^5.5.0",
       "typeface-roboto": "0.0.75",
       "web-vitals": "^0.2.2"
+    },
+    "eslintConfig": {
+      "extends": ["react-app", "react-app/jest"]
     }
   }
 }

packages/eslint-config-react-app/jest.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+// We use eslint-loader so even warnings are very visible.
+// This is why we prefer to use "WARNING" level for potential errors,
+// and we try not to use "ERROR" level at all.
+
+module.exports = {
+  plugins: ['jest'],
+  overrides: [
+    {
+      files: ['**/__tests__/**/*', '**/*.{spec,test}.*'],
+      env: {
+        'jest/globals': true,
+      },
+      // A subset of the recommended rules:
+      // https://github.com/jest-community/eslint-plugin-jest#rules
+      rules: {
+        'jest/expect-expect': 'warn',
+        'jest/no-identical-title': 'warn',
+        'jest/valid-describe': 'warn',
+        'jest/valid-expect': 'warn',
+        'jest/valid-expect-in-promise': 'warn',
+      },
+    },
+  ],
+};