feat: add style recommended config

Author: SimenB

README.md

@@ -72,6 +72,17 @@ config file:
 }
 ```
 
+### Style
+
+This plugin also exports a configuration named `style`, which adds some
+stylistic rules, such as `prefer-to-be-null`, which enforces usage of `toBeNull`
+over `toBe(null)`. All rules included are:
+
+- `prefer-to-be-null`
+- `prefer-to-be-undefined`
+- `prefer-to-contain`
+- `prefer-to-have-length`
+
 See
 [ESLint documentation](http://eslint.org/docs/user-guide/configuring#extending-configuration-files)
 for more information about extending configuration files.

index.js

@@ -49,6 +49,15 @@ module.exports = {
         'jest/valid-expect-in-promise': 'error',
       },
     },
+    style: {
+      plugins: ['jest'],
+      rules: {
+        'jest/prefer-to-be-null': 'error',
+        'jest/prefer-to-be-undefined': 'error',
+        'jest/prefer-to-contain': 'error',
+        'jest/prefer-to-have-length': 'error',
+      },
+    },
   },
   environments: {
     globals: {